how to find primary research articles on pubmed

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PubMed User Guide

Last update: February 14, 2024

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How can I get the full text article ? What if the link to the full text is not working ?
How do I search by author ?
How do I search by journal name ?
How do I find a specific citation ? I have some information such as the author, journal name, and publication year.
I retrieved too many citations. How can I focus my search ?
I retrieved too few citations. How can I expand my search ?
How do I find consumer health information about a disease or condition?
How do I find systematic reviews ?
Are there tools to help with clinical searches or finding medical genetics information?
I’m not finding what I need. How does a PubMed search work ?
Can you explain what is shown on the search results ?
How do I display an abstract ?
How can I save my results ?
Can I receive email updates when new results are available for my search ?
How do I report an error or duplicate citation in PubMed?
How can I cite an article or export citations to my citation management software program ?
How do I get a link to bookmark or share my PubMed search ?
How can I download PubMed?
Is there a guide to NLM resources for MEDLINE/PubMed ?
Where can I find further assistance and training ?

Search PubMed

How do i search pubmed, i retrieved too many citations. how can i focus my search, i retrieved too few citations. how can i expand my search, find a specific citation, searching by author, searching by journal, searching by date, searching for a phrase, truncating search terms, combining search terms with boolean operators (and, or, not), using search field tags, proximity searching.

Identify the key concepts for your search.
Enter the terms (or key concepts) in the search box.
Press the Enter key or click Search.

For many searches, it is not necessary to use special tags or syntax. PubMed uses multiple tools to help you find relevant results:

Best Match sort order uses a state-of-the-art machine learning algorithm to place the most relevant citations at the top of your results.
An autocomplete feature displays suggestions as you type your search terms. This feature is based on PubMed query log analysis described in " Finding Query Suggestions for PubMed ."
A spell checking feature suggests alternative spellings for search terms that may include misspellings.
A citation sensor displays suggested results for searches that include terms characteristic of citation searching, e.g., author names, journal titles, publication dates, and article titles.

To limit the number of search results:

Replace general search terms with more specific ones (e.g., low back pain instead of back pain).
Include additional terms in your query.
Use the sidebar filters to restrict results by publication date, full text availability, article type, and more.
On the abstract page for a citation, see the Similar Articles section for a pre-calculated set of additional PubMed citations closely related to that article.
Remove extraneous or specific terms from the search box.
Try using alternative terms to describe the concepts you are searching.

Paste the article title into the search box, or enter citation details such as the author, journal name and the year the article was published in the search box and the PubMed citation sensor will automatically analyze your query for citation information to return the correct citation. The citation sensor incorporates a fuzzy matching algorithm and will retrieve the best match even if a search includes an incorrect term. You do not need to use field tags or Boolean operators.

Enter the author’s last name and initials without punctuation in the search box, and click Search.

If you only know the author’s last name, use the author search field tag [au], e.g., brody[au].

Names entered using either the lastname+initials format (e.g., smith ja) or the full name format (john a smith) and no search tag are searched as authors as well as collaborators, if they exist in PubMed.

Enter a full author name in natural or inverted order, e.g., julia s wong or wong julia s.
Prior to 2002, full author names were not included on PubMed citations, so full author name searches will only retrieve citations from 2002 forward, when the full author name was published in the article.
A comma following the last name for searching is optional. For some names, however, it is necessary to distinguish which name is the last name by using the comma following the last name, e.g., james, ryan.
Omit periods after initials and put all suffixes at the end, e.g., vollmer charles jr

Initials and suffixes are not required. If you include a middle initial or suffix, you will only retrieve citations for articles that were published using the middle initial or suffix.

More information about author searching:

To search by author using the search builder, click Advanced search and then select Author from the All Fields menu. The author search box includes an autocomplete feature.
You may click an author link on the abstract display to execute a search for the author in PubMed. Results will display using a ranking algorithm if the author name is computationally similar for additional PubMed citations.
If an author name includes only stopwords , use the author search field tag [au] to search in combination with other terms, e.g., just by[au] seizure.
Author names are automatically truncated to account for varying initials and designations such as Jr. To turn off the truncation, use double quotes around the author's name with the author search field tag [au], e.g., "smith j"[au].
Use the search field tag [1au] to search for the first personal author or [lastau] to search for the last personal author name in a citation.

For additional information on author names in PubMed, please see the journal article, " Author Name Disambiguation for PubMed ."

Enter one of the following in the search box:

full journal title (e.g., molecular biology of the cell)
title abbreviation (e.g., mol biol cell)
ISSN number, a standardized international code (e.g., 1059-1524)

More information about journal searching:

To search by journal using the search builder, click Advanced search and then select Journal from the All Fields menu. The journal search box includes an autocomplete feature.
Click Journals in NCBI Databases on the PubMed homepage.
Enter the journal name and click Search.
Use the journal search field tag [ta] to limit your search to the journal only, e.g., gene therapy[ta], scanning[ta]
Searching with the full journal title or abbreviation is recommended for complete retrieval of indexed items; older citations may not have an ISSN.
If a journal title or abbreviation includes a special character (e.g., parentheses, brackets, &), enter the title or abbreviation without the special characters. For example, to search by the journal abbreviation j hand surg [am], enter j hand surg am.
Searching for a journal will automatically map to the official journal title and the title associated with an alternative title, if one exists. To turn off this automatic mapping enter the journal in double quotes and tag with [ta], e.g., "science"[ta].

A list of journals included in PubMed is available by FTP.

Using the results timeline

Using the search builder, searching by a single date in the search box, searching for a date range in the search box, searching for a relative date range.

Click and drag the sliders on the Results By Year timeline to change the date range for your search.

Note: The Results By Year timeline counts all publication dates for a citation as supplied by the publisher, e.g., print and electronic publication dates. These dates may span more than one year; for example, an article that was published online in November 2018 and published in a print issue in January 2019. This means the sum of results represented in the timeline may differ from the search results count.

Click Advanced search and use the search builder.
Select a date field from the All Fields menu, e.g., Date – Publication, and enter a single date or a date range in the fill-in-the-blank boxes. Month and day are optional. If you want to search for a date range up to the current date, do not edit the ‘Present’ date box.
Add the date from the builder to the query box.
Once you have finished adding terms to the query box, click Search (or Add to History) to run the search.

Enter dates using the format yyyy/mm/dd [date field]. The month and day are optional.

Use a Boolean operator when combining a date with other search terms.

Use the Boolean operator AND to limit your search to a specific publication date.

The available date fields are:

Date of Publication [dp] - Date searching includes both print and electronic dates of publication. Searching for a single date does not include items when the electronic date of publication is after the print date.
Electronic Date of Publication (if applicable) [epdat]
Print Date of Publication (if applicable) [ppdat]
Entry Date [edat] - Date used for PubMed processing, such as “Most Recent” sort order.
MeSH Date [mhda] - The date the citation was indexed with MeSH terms.
Create Date [crdt] - The date the PubMed record was first created.

Enter date ranges using a colon (:) between each date followed by a [date field].

Use a Boolean operator when combining a date range with other search terms.

Use the Boolean operator AND to limit your search to a date range.

Comprehensive searches for a full year should be entered as 2000:2000[dp] rather than 2000[dp] to retrieve citations with a different print and electronic year of publication.

Date range searching includes both print and electronic dates of publication.

Use the following format to search for a relative date range:

term="last X days" [date field]
term="last X months" [date field]
term="last X years" [date field]

where X is the number of days, months or years immediately preceding today’s date and [date field] is the date field tag: [dp], [edat] or [crdt].

The relative date range search for publication dates will also include citations with publication dates after today's date; therefore, citations with publication dates in the future will be included in the results.

You can use filters to narrow your search results by article type , text availability , publication date , species , article language , sex , age , and other .

To apply a filter:

Run a search in PubMed.
Click the filter you would like to activate from the sidebar. A check mark will appear next to the activated filter(s).
Subsequent searches will be filtered until the selected filters are turned off, or until your browser data is cleared.

The most popular filters are included on the sidebar by default. To display additional filters on the sidebar:

Click the "Additional filters" button.
A pop-up menu will appear showing the available filters for each category: article type, species, article language, sex, age, and other.
Choose a category from the list of options on the left side of the menu: Article Type, Species, etc.
Within each category, select the filters you would like to add to the sidebar.
Click Show. This will close the pop-up menu and display your selections on the sidebar with the other filters.
If you would like to cancel your selections, click Cancel or click on the X in the upper right corner to close the pop-up and return to your search results.
To apply the filter(s) to your search, click the filter(s) on the sidebar.

More information about filters:

When filters are selected a "Filters applied" message will display on the results page.
Click an applied filter to turn it off.
To turn off all applied filters, click the "Clear all" link or the "Reset all filters" button.
Citations may be excluded for some filter selections because they have not yet completed the MEDLINE indexing process.
You can activate additional filters with My NCBI filters .
See Filter search strategies for the equivalent PubMed query for each filter.

Article type

Select article types to narrow your results based on the type of material the article represents, such as: Clinical Trial or Review.

You can add more article types to the sidebar using the Additional Filters button. The complete list of publication types found in PubMed is available.

These filters may exclude some citations that have not yet completed the MEDLINE indexing process because they rely on the Publication Type [pt] data for the citation; publication type data may be supplied by the publisher or assigned during the MEDLINE indexing process. However, the Systematic Review article type filter uses a search strategy to capture non-MEDLINE citations and citations that have not yet completed MEDLINE indexing in addition to citations assigned the systematic review publication type.

Systematic reviews

To search for systematic reviews in PubMed, use the Systematic Review article type filter on the sidebar, or enter your search terms followed by AND systematic[sb] in the search box. For example, lyme disease AND systematic[sb].

The Systematic Review filter uses a search strategy in addition to the Systematic Review publication type [pt] to find systematic reviews in PubMed. To limit your search to only those citations with the Systematic Review publication type, use the publication type search tag[pt], i.e., systematic review[pt]; however, this may exclude some relevant citations that have not yet completed the MEDLINE indexing process.

Text availability

To filter your results to only citations that include a link to full text, a link to free full text, or an abstract, click the appropriate selections.

Alternatively, you may search for citations with links to full text, free full text or include an abstract using the values: full text[sb], free full text[sb], or 'hasabstract'. No search field tag is required for hasabstract. You may also search for all MEDLINE citations with a structured abstract with ‘hasstructuredabstract’.

Note: Most citations in PubMed to articles published before 1975 do not include abstracts.

Publication date

To filter your results by Publication Date, click 1 year, 5 years, 10 years, or enter a custom range. These filters include both electronic and print publication dates.

Species selections restrict your results to human or animal studies.

You can add species filters to the sidebar using the Additional Filters button.

These filters may exclude some citations because they have not yet completed the MEDLINE indexing process.

Article language

Language filters restrict your search to articles published in the selected language(s). You can add language filters to the sidebar using the Additional Filters button.

By default, PubMed displays English language titles and abstracts when provided by the publisher. Check the Abstract display for links to view the abstract in other languages (when available).

Sex restricts your search results to a specific sex for an animal or human study.

You can add sex filters to the sidebar using the Additional Filters button.

This filter may exclude some citations because they have not yet completed the MEDLINE indexing process.

Age filters restrict results to a specific age group for a human study.

You can add age filters to the sidebar using the Additional Filters button.

Age filters include:

Child: birth-18 years
Newborn: birth-1 month
Infant: birth-23 months
Infant: 1-23 months
Preschool Child: 2-5 years
Child: 6-12 years
Adolescent: 13-18 years
Adult: 19+ years
Young Adult: 19-24 years
Adult: 19-44 years
Middle Aged + Aged: 45+ years
Middle Aged: 45-64 years
Aged: 65+ years
80 and over: 80+ years

Other filters & more subsets

Exclude preprints.

The Exclude preprints filter can be added to the sidebar using the Additional Filters button. Alternatively, you can exclude preprints from your search results by including NOT preprint[pt] at the end of your query.

See Preprints for more information about preprint citations in PubMed.

MEDLINE Subset

The MEDLINE filter can be added to the sidebar using the Additional Filters button. To use this filter in a query, add medline[sb] to your search. The MEDLINE filter limits results to citations that are indexed for MEDLINE .

PubMed Central Subset

To restrict retrieval to citations that have a free full text article available in PubMed Central (PMC), search "pubmed pmc"[sb].

Use the PMID/PMCID/NIHMSID Converter to convert IDs for publications referenced in PubMed and PMC. To retrieve citations that include an NIHMS ID use the query, hasnihmsid.

Citation Status Subsets

The citation status indicates the internal processing stage of an article in the PubMed database (see PubMed Citation Status Subsets ).

To search for a particular citation status, enter one of the search terms below followed by the [sb] search tag:

pubmednotmedline

To search for the total number of PubMed citations, enter all[sb] in the search box.

Ahead of Print Citations

Publishers may submit citations for articles that appear on the web prior to their publication in final or print format. To search for these ahead-of-print citations, enter pubstatusaheadofprint.

Many phrases are recognized by the subject translation table used in PubMed's Automatic Term Mapping (ATM) . For example, if you enter fever of unknown origin, PubMed recognizes this phrase as a MeSH Term.

You can bypass ATM and search for a specific phrase using the following formats:

If you use quotes and the phrase is not found in the phrase index , the quotes are ignored and the terms are processed using automatic term mapping. The message "Quoted phrase not found in phrase index" will display at the top of your search results.
If you use a search tag and the phrase is not found in the phrase index , the phrase will be broken into separate terms, e.g., "psittacine flight" is not in the phrase index, so a search for psittacine flight[tw] is broken up and translated as: ((("psittaciformes"[MeSH Terms] OR "psittaciformes"[All Fields]) OR "psittacine"[All Fields]) OR "psittacines"[All Fields]) AND "flight"[Text Word]
If you use a hyphen and the phrase is not found in the phrase index , the search will not return any results for that phrase.

When you enter search terms as a phrase, PubMed will not perform automatic term mapping that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy. For example, "health planning" will include citations that are indexed to the MeSH term, Health Planning, but will not include the more specific terms, e.g., Health Care Rationing, Health Care Reform, Health Plan Implementation, that are included in the automatic MeSH mapping.

Phrase index

PubMed uses a phrase index to provide phrase searching. To browse the phrase index, use the Show Index feature included in the Advanced Search builder: select a search field, enter the beginning of a phrase, and then click Show Index.

Quoted phrase not found

Phrases may appear in a PubMed record but not be in the phrase index. To search for a phrase that is not found in the phrase index, use a proximity search with a distance of 0 (e.g., "cognitive impairment in multiple sclerosis"[tiab:~0] ); this will search for the quoted terms appearing next to each other, in any order.

Automated processes regularly add new phrases to the index based on standard criteria such as phrase frequency and length. If you would like to request a phrase be added to the phrase index, please write to the NLM Help Desk .

To search for all terms that begin with a word, enter the word followed by an asterisk (*): the wildcard character.

To search for a phrase including a truncated term, use the following formats:

Enclose the phrase in double quotes: "breast feed*"
Use a search tag: breast feed*[tiab]
Use a hyphen: breast-feed*

At least four characters must be provided in the truncated term.

The truncated term must be the last word in the phrase.

Truncation turns off automatic term mapping and the process that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy. For example, heart attack* will not map to the MeSH term Myocardial Infarction or include any of the more specific terms, e.g., Myocardial Stunning; Shock, Cardiogenic.

PubMed applies an AND operator between concepts, e.g., "vitamin c common cold" is translated as vitamin c AND common cold. Enter Boolean operators in uppercase characters to combine or exclude search terms:

AND retrieves results that include all the search terms.
OR retrieves results that include at least one of the search terms.
NOT excludes the retrieval of terms from your search.

PubMed processes searches in a left-to-right sequence. Use parentheses to "nest" concepts that should be processed as a unit and then incorporated into the overall search.

PubMed uses automatic term mapping to identify concepts. For example, for the search air bladder fistula, PubMed will search "air bladder" as a phrase. If you do not want this automatic phrase parsing, enter each term separated by the Boolean operator AND, e.g., air AND bladder AND fistula.
Search Details show how a search was translated.

You can search for a term in a specific field by including a search field tag after the term; for example, UCLA[ad] will search for the term “UCLA” in the affiliation field only.

More information about using search field tags:

The search field tag must be enclosed in square brackets.
Case and spacing do not matter: crabs [mh] = Crabs[mh].
Search field tags turn off Automatic Term Mapping (ATM) , limiting your search to the specified term only.
Using a search field tag after multiple terms will attempt to search those terms as a phrase : kidney allograft[tiab].
To search multiple terms in the same field, each term must be tagged individually: covid-19[ti] vaccine[ti] children[ti].
The Advanced Search builder can help you search for terms in specific fields and build large, complex search strings.

Search field tags

Affiliation [ad], all fields [all], article identifier [aid], author [au], author identifier [auid], book [book], comment correction type, completion date [dcom], conflict of interest statement [cois], corporate author [cn], create date [crdt], ec/rn number [rn], editor [ed], entry date [edat], filter [filter] [sb], first author name [1au], full author name [fau], full investigator name [fir], grants and funding [gr], investigator [ir], isbn [isbn], journal [ta], language [la], last author name [lastau], location id [lid], mesh date [mhda], mesh major topic [majr], mesh subheadings [sh], mesh terms [mh], modification date [lr], nlm unique id [jid], other term [ot], pagination [pg], personal name as subject [ps], pharmacological action [pa], place of publication [pl], pmcid and mid, pmid [pmid], publication date [dp], publication type [pt], publisher [pubn], secondary source id [si], subset [sb], supplementary concept [nm], text words [tw], title/abstract [tiab], transliterated title [tt], volume [vi].

You can use proximity searching to search for multiple terms appearing in any order within a specified distance of one another in the [Title], [Title/Abstract], or [Affiliation] fields.

To create a proximity search in PubMed, enter your terms using the following format:

"search terms"[field:~N]

There is no limit to the number of words you can search together in proximity; however, the more terms you enter, the more restrictive your search becomes. Using the Boolean operator AND to combine terms may be more appropriate than combining many terms into one proximity search.
Proximity searching is only available in the Title , Title/Abstract , and Affiliation search fields.
You can use the full search field tags [Title], [Title/Abstract], and [Affiliation], or the abbreviated versions [ti], [tiab], and [ad].
What N value to use will depend on your search. Try changing the N value and comparing the results to find what works best for your search.
A higher N creates a broader, more comprehensive search; this will typically retrieve more results overall, but some of these results may be less relevant. Using the Boolean operator AND to combine terms may be more appropriate than proximity searching with a large N value.
A lower N creates a narrower, more precise search; this will typically retrieve fewer results that are highly relevant, but may exclude other relevant results.
If N=0, the quoted terms will appear next to each other--with no other words in between.
For the affiliation field only, an N value of 1,000 or less will search for the double quoted terms together within the same affiliation, rather than spread across all affiliations on the record. See Affiliation [ad] for an example proximity search in the affiliation field and more information about searching for affiliations.

More information about proximity searching:

Results will include your quoted terms in any order. If you would like to search for an exact phrase with terms appearing in a specific order, use a phrase search instead.
Automatic Term Mapping is not applied to the quoted terms.
Proximity searching is not compatible with truncation (*). If the double quoted terms in a proximity search include a wildcard (*), the proximity operator will be ignored.
You can combine proximity searches with other terms using Boolean operators; for example, "hip pain"[Title:~4] AND stretching
Booleans and stopwords included in quoted terms for proximity search are searched like regular keywords.

Search PubMed for citations with the terms "rationing" and "healthcare" appearing within 2 words of each other--in any order--in the Title field:

Search results may include: rationing healthcare, healthcare rationing, rationing of healthcare, rationing in healthcare, rationing universal healthcare, rationing strategies in healthcare, rationing limited healthcare… and more.

Search PubMed for citations with the terms "patient," "physician," and "relationship" appearing next to each other—in any order—in the Title/Abstract fields:

Since N=0, the quoted terms must appear next to each other with no other words in between them, although they can still appear in any order.

You can build queries that combine proximity searches with other terms using Boolean operators (AND, OR, NOT):

Display, Sort, and Navigate

Understanding your search results, display an abstract, changing the display format of search results.

Showing more results

Sorting your results

Finding the full text article, similar articles, grants and funding, navigating searches with more than 10,000 results, discovering related data in ncbi databases, find related resources using linkout, reporting broken or problem links.

Citations are initially displayed 10 items per page and sorted by Best Match.

By default, PubMed search results are displayed in a summary format and include snippets from the citation abstract. Snippets and highlighted terms are selected based on relatedness to your query.

To see the abstract for an individual citation, click the title of the citation to go to its abstract page.

Journal names are shown using the journal title abbreviation. When viewing citations in Abstract format, you can mouseover a journal’s title abbreviation to display the full journal name.

Click the title of the citation to go to its abstract page, or change the search results display to Abstract format using the Display options button in the upper right corner of the search results page.

PubMed may include non-English abstracts if supplied by the publisher. The abstract text defaults to English when a citation has an accompanying non-English abstract. Links to display the additional language(s) are available on the Abstract display. To retrieve citations with non-English abstracts, use the query hasnonenglishabstract.

Results are displayed in the summary format by default, except a single citation result will go directly to the abstract page. You can change the results format using the Display options button:

Click the Display options button in the upper right corner of the search results page
Select the display format you would like to use
Results will be displayed in the new format

Selecting one or more items and changing the display format will display only the selected result(s) in the new format.

By default, the summary format includes snippets from the citation abstract. You can turn off snippets under Display options by deselecting Abstract snippets.

The results page indicates the total number of items retrieved.

Ten items are displayed per page by default. You can change the number of items displayed per page using the Display options button:

Select the number of items to display per page: 10, 20, 50, 100, or 200
Your selection will be active for subsequent searches until your browser cookies are cleared.

Click "Show more" to display the next page of results, or click "Jump to page" to navigate directly to a specific page of results.

The default sort order in PubMed is Best Match. You can use the "Sort by" drop-down menu at the top of the search results page to change the sort order.

If you change the sort order, your new selection will be active for subsequent searches until your browser cookies are cleared.

Sort orders

You can sort your search results by:

Best Match: The Best Match sort order is based on an algorithm that analyzes each PubMed citation found with your search terms. For each search query, "weight" is calculated for citations depending on how many search terms are found and in which fields they are found. In addition, recently-published articles are given a somewhat higher weight for sorting. The top articles returned by the weighted term frequency algorithm above are then re-ranked for better relevance by a new machine-learning algorithm. Please see the Algorithm for finding best matching citations in PubMed for more information.
Most Recent: Citations sorted by Most Recent are displayed in reverse date added order: last in, first out. The Most Recent date is the date a record was initially added to PubMed, not the publication date. The secondary sort is PMID.
Publication Date: Citations sorted by Publication Date are displayed in reverse chronological order: newest to oldest. Citations with more than one publication date, such as electronic and print, are sorted by their earliest publication date. Publication dates without a month are set to January, multiple months (e.g., Oct-Dec) are set to the first month, and dates without a day are set to the first day of the month. Dates with a season are set as: winter = January, spring = April, summer = July and fall = October.
First Author: Citations are sorted alphabetically by first author name. The secondary sort order within a group with the same first author is PMID.
Journal: Citations are sorted alphabetically by journal name. The secondary sort order within a group with the same journal name is PMID.

Reverse sort order

When sorting by Most Recent, Publication Date, First Author, or Journal, you can reverse the sort order by clicking the up/down arrow next to the selected sort option to toggle between ascending or descending order.
The reverse sort option will not display when Best Match sort order is selected.

Computed author sort

Clicking an author name link on the abstract display runs a search for the author in PubMed. If an author name is computationally similar with an author name for additional PubMed citations, the results will display those citations first, in ranked order, followed by the non-similar citations. Author name disambiguation details are available in Liu W and Wilbur WJ .

PubMed records contain citation information (e.g., title, authors, journal, publication date) and abstracts of published articles and books. PubMed search results do not include the full text of the journal article, but the abstract view in PubMed includes links to the full text from other sources when available, such as the publisher’s website or the PubMed Central (PMC) database. The full text journal site may require a fee or subscription, however online journals sometimes provide free access. Access may also be available through your organization, or local medical library.

You may be able to obtain free copies of full text articles in these ways:

Free full text filter

On the filter sidebar, click "Free full text" to narrow results to resources that are available for free on the web, including PubMed Central, Bookshelf, and publishers' websites. Alternately, include free full text[Filter] in your query.

PubMed Central

When full text is available in PubMed Central (PMC) , the "Free in PMC" icon will appear on the citation's abstract display under Full Text Links. Click the icon to view the article in PMC.

PubMed Central (PMC) is the U.S. National Institutes of Health (NIH) free digital archive of biomedical and life sciences journal literature.

From the publisher

Journal publishers or related organizations may provide access to articles for free, for free after registering as an individual or guest, or for a fee. When provided by the publisher or other organization, icons linking to these sources can be found on the citation's abstract display under the "Full Text Links" and/or "LinkOut" sections. Icons will often indicate free full text when the article is available for free.

Note: When you click a full text icon or link in PubMed, you leave PubMed and are directed to the full text at an external provider's site. NCBI does not hold the copyright to this material, and cannot give permission for its use. Users should review all copyright restrictions set forth by the full text provider before reproducing, redistributing, or making commercial use of material accessed through LinkOut.

Please see the Copyright and Disclaimers page for additional information.

If you are affiliated with a hospital, university, or other institution

Your local medical library is your best option. If you see icons for your library on the abstract view this indicates that your library provides a link to the article, has the journal in its collection, or may otherwise obtain the article for you through interlibrary loan. If your library does not have access to the article you need, ask a librarian about ordering the article from another institution.

Local library

Some local libraries have copies of medical journals or can get a copy of an article for you. Ask your local librarian about inter-library loan options and fees.

PubMed abstracts include figures when the full text article is available in PubMed Central (PMC) . Click the thumbnail to view a larger version of the image, caption, and link to the figure and copyright information in PMC.

The abstract page for a citation includes links to PubMed citations for similar articles. The "See all similar articles" link will retrieve a pre-calculated set of PubMed citations that are closely related to the selected article:

Similar articles are displayed in ranked order from most to least relevant, with the "linked from" citation displayed first.
Similar articles are generated by comparing words from the title, abstract, and MeSH terms using a word-weighted algorithm.
Filters are not activated for similar articles.
You can refine the list of similar articles using your search History , where the similar articles retrieval is represented as a list of PMIDs. Use this search number in a search. Refining the list removes the ranked order and may remove citations that are most relevant.

See Computation of similar articles for more information.

PubMed abstracts include links to other resources citing the current item. "Cited by" is generated using data submitted by publishers and from NCBI resources, when available. "Cited by" may not be a complete list of works citing a particular item.

PubMed abstracts include references when available. Reference lists are available for citations to full text articles included in the open access subset of PMC and for citations where the publisher supplied references in the citation data sent to PubMed.

PubMed displays grant numbers, contract numbers, and intramural research identifiers that have been associated with a publication by:

Publishers when depositing data in PubMed and PubMed Central;
depositing a manuscript through the NIH Manuscript Submission (NIHMS) or Europe PMC Plus system; or
when adding a publication to My Bibliography ; and/or
NLM text mining and indexing processes.

A grant award or contract may be acknowledged in an article and, therefore, displayed in PubMed, for various reasons, including support for activities that contributed directly to the publication as well as support for the generation of an underlying dataset or another shared resource. Additionally, some articles may not explicitly acknowledge intramural research support, yet the authors may be affiliated with a funding agency and may have associated their intramural support with a PubMed record at the time of manuscript deposit to PMC.

Funding information in PubMed is collected in or converted to a standardized format when possible to enable broad discovery and impact monitoring. For example, if a publication acknowledges support from NIH grant number 1R01 GM987654-01-A1 or GM987654 or ROI GM987654 in a publication, in PubMed the funding information would be normalized to R01 GM987654, consistent with NIH requirements for proper grant number format. Funding associations made in a manuscript submission, grant reporting, or indexing system use standardized project identifiers provided to NLM by the organization administering the funding. To learn about searching funding information, see the search field section on Grants and funding [gr] .

The scope of funding information included in PubMed has expanded over time to support the public access policies of NIH and other funding organizations . Since 1981, NLM has included grant or contract numbers or both that designate financial support by any agency of the United States Public Health Service (PHS), including NIH. Until 2000, only up to three grant numbers were included. Beginning in March 2006, funding information was expanded in PubMed to include grant, contract, and intramural funding assertions made in NIHMS and My Bibliography to support the NIH Public Access Policy. Publishers have been able to supply funding information directly to PubMed since January 2017. For more information on the history of funding information in PubMed, see the Grant Number section of MEDLINE/PubMed Data Element (Field) Descriptions .

Reporting funding information errors

Some publications may be inadvertently linked to the wrong funding information. For example, the association of a publication to NIH-funded extramural research requires that the author(s) acknowledge NIH support in the article and that the acknowledgement be in a form that can be readily associated with a specific grant or contract. Variations in the format used to cite NIH funding may lead to either an inability to make an association or erroneous matches of publications to grants and contracts.

If you identify an error in funding information associated with a PubMed record, please contact the NLM help desk . NLM will not remove funding associations that reflect the acknowledged funding in the article without a published correction to ensure alignment with the scientific record. If an award association was provided by the author, principal investigator, or project director in My Bibliography or the NIHMS for formal NIH progress and public access compliance reporting, removing the association requires the principal investigator be notified and confirm the lack of direct support.

PubMed can display up to 10,000 results. The following options can help you navigate searches with more than 10,000 results:

Reverse the sort order to see the last results first.
Divide the result set into smaller chunks using the results timeline or custom date range filter .
Adjust your search to retrieve fewer results.
For programmatic use and bulk downloads, PubMed data is available via FTP .

When available, links to other related NCBI databases are included on a citation's Abstract page under the Related information section. The complete list of database options is provided in Entrez Link Descriptions .

MEDLINE indexed citations include additional supplemental information on the Abstract page such as MeSH terms, publication types, and substances with links to search for these data in PubMed and the MeSH Database.

To simultaneously search all NCBI databases, use the NCBI Search page .

Most PubMed records include LinkOut resources to a variety of websites including publishers, aggregators, libraries, biological databases, and sequence centers. LinkOut resources link to providers’ sites to obtain the full text of articles or related information, e.g., consumer health. There may be a charge to access the text or information from a provider's site.

To view LinkOut resources, navigate to the LinkOut section at the end of an individual citation's abstract page.

To find citations with links to free full text articles, apply the "Free full text" filter to your search results.

To find citations with links to full text articles, enter search terms followed by AND full text[sb].

Cite, Save, and Share

Save citations temporarily using the clipboard, save citations indefinitely using my ncbi collections, save citations as a text file, cite an article, export citations into citation management software, email citations, create an email alert for a search, create an rss feed for a search, print your search results, get a permalink to bookmark or share your search, download pubmed data.

The Clipboard provides a place to collect up to 500 items from one or more searches. Items saved to the Clipboard are stored in your browser cookies and will expire after 8 hours of inactivity. If you would like to save items for longer than 8 hours or to view on another device, please use Send to: Collections .

To add items to the Clipboard:

Use the check boxes to select items from your search results. To save all results (up to a maximum of 500), do not tick any check boxes.
Use the Send to button and choose Clipboard.
If no items were selected, a drop-down menu of options will display where you may add selected items, all results on the page, or all results (up to a maximum limit of 500 citations) to the Clipboard.
An individual item can also be added to the Clipboard from its abstract page.
To view your selections, click the Clipboard link under the Search bar. This link will only appear after one or more items have been added to the Clipboard; the link is not present when the Clipboard is empty.

To delete items from the Clipboard:

On the Clipboard page, click "Remove from Clipboard" below each item to delete the item from the Clipboard.
Select one or more items using the check boxes next to each item, then click "Remove selected items."
To delete all items from the Clipboard, click "Remove all."

More information about the Clipboard:

Citations added to the Clipboard are marked with the message "Item in Clipboard" in search results.
The maximum number of items that can be sent to the Clipboard is 500. If you select Clipboard from send to without selecting citations, PubMed will add all (up to 500 citations) of your search results to the Clipboard.
The Clipboard will not add a citation that is currently in the Clipboard; it will not create duplicate entries.
Your web browser must accept cookies to use the Clipboard.
Citations in the Clipboard are represented by the search number #0, which may be used in Boolean search statements. For example, to limit the citations you have collected in the Clipboard to English language articles, use the following search: #0 AND english [la]. This does not affect or replace the Clipboard contents.

Search results can be saved in My NCBI using the Collections feature. There is no limit to the number of collections you may store in My NCBI. In addition, collections can be made public to share with others.

To save results to a new collection:

Sign into My NCBI. Run a search in PubMed.
Use the check boxes to select items from your search results or Clipboard. To save all results (up to a maximum of 1,000), do not tick any check boxes.
Use the Send to button and choose Collections.
If no items were selected, a drop-down menu of options will display where you may add selected items, all results on the page, or all results (up to a maximum limit of 1,000 citations) to a Collection.
An individual item can also be added to a Collection from its abstract page.
Choose Create a new collection.
Name your collection using a short, meaningful title. The name must be unique and less than 100 characters. Identical names for different Collections are not allowed.
Click Add to finish.

As you continue to build collections, you may want to add new items to an existing collection. To add search results to an existing collection:

Follow steps 1 - 4 above. Add to an existing collection will be the default selection.
Use the pull-down menu to choose a collection.

For more information on viewing, sorting, editing, merging, sharing, and deleting collections, see Collections in My NCBI Help.

Use the Save button to download citations to a text file.

Use the check boxes to select citations from your search results or Clipboard. You may move to other pages to continue your selections. If you do not make any selections, you can choose to save “All results on this page” or “All results” from the Save menu.
Selection: The number of selected items will be shown, for example: Selection (87).
All results on this page
All results (up to a maximum of 10,000 citations)
Format: Summary (text), PubMed , PMID list, Abstract (text), or CSV
Click Create file.
Your web browser will prompt you to save the file on your computer.

More information about saving citations to a file:

Saving a large set of results may take several minutes.
To save citations in HTML format, use the "Save" or "Save as" function of your browser and change the file extension to html. When saving as HTML, only those citations displayed on the page will be saved; therefore, consider showing more results .

The Cite button makes it easy to retrieve styled citations that you can copy and paste into a document, or download an .nbib file to use with your reference manager software.

Using the Cite button for an item will open a pop-up window where you can copy the citation formatted in four popular styles: AMA (American Medical Association), MLA (Modern Language Association), APA (American Psychological Association), or NLM (National Library of Medicine). You can also download the citation as an .nbib file, which most bibliographic reference management software can import.

Note: In all citation styles, there are certain capitalization rules that machines cannot handle. For example, there is no way to identify proper nouns, acronyms, abbreviations, etc., that is 100% accurate and complies with all rules at all times. Capitalization of article titles and other citation elements should be checked for compliance with a particular reference style when required.

To export multiple citations: follow the instructions for saving citations as a text file and choose the format Summary (text) to save a list of citations in NLM style, or follow the instructions to export citations into your citation management software program .

Use Send to: Citation Manager to export citations as an .nbib file that can be used by many citation management programs:

Use the check boxes to select citations from your search results or Clipboard. You may move to other pages to continue your selections. Alternately, you can choose to save all results on this page or all results from the Send to: Citation Manager menu.
Click Send to and choose Citation Manager.
Confirm the citations you want to export: selection, all results on this page, or all results (up to a maximum of 10,000).
Import this saved file into your citation management program.

You can also download an .nbib file for individual citations using the Cite button.

Questions regarding citation management software should be directed to the respective companies.

Use the check boxes to select citations from your search results or Clipboard. You may move to other pages and continue your selections. You may also choose to email all citations shown on the page without making any selections.
Click the Email button.
Enter an email address. Select which citations to send and the format.
Click Send email. The system returns you to your results page and displays a confirmation e-mail sent message.

More information about emailing citations:

Your citations will be sent from the NCBI automatic mail server with the sender's email address [[email protected]]. Do not reply to this message, as this is not a functioning customer service email address and is not monitored.
The CAPTCHA image does not display for users who are signed in to My NCBI.

Click "Create alert" under the search bar to create an automatic email update for searches. You must sign in to My NCBI to use this feature. See Saving and Managing Searches for more information.

Click on Create RSS under the search box at the top of the page to create an RSS feed for your search.

The RSS feed name will default to the search terms. You can edit the RSS feed name as needed.
Use the pull-down menu to select the number of items displayed. You may manually edit the limit= parameter in the RSS feed link created in Step 4 to display up to a maximum of 1000 items. Please note that increasing this limit will also increase the loading time.
Click the Create RSS button.
The RSS Feed Link will appear; click on Copy to copy the link.
Use this link with your feed reader or other application.

Use the print function of your web browser. To print citations from different searches, save the citations in PubMed’s Clipboard , and then print.

Changing the display format

To get the URL for an individual citation, copy the permalink for the citation under "Share."

To get the URL for your search results, copy the URL from your web browser's address bar or bookmark the URL using your web browser's bookmark function.

To create a URL manually:

Use the base URL: https://pubmed.ncbi.nlm.nih.gov/?term=search
Replace “search” in the base URL with your query terms
Escape spaces by converting them to plus signs (+); for example, Biochem Soc Trans should be entered as: Biochem+Soc+Trans

The number of characters you can use may be limited by your browser’s maximum URL length (which may be different for each browser).

Search PubMed for articles about antioxidant and chocolate:

Optional search parameters:

format=summary, abstract, pubmed, pmid
sort=relevance, date, pubdate, fauth, jour
sort_order=asc
size=10, 20, 50, 100, 200

Search PubMed for articles about breast cancer, sorted by ascending publication date (oldest to newest), and display 50 citations per page:

Advanced Search

Searching in a specific field, browsing the index of terms, previewing the number of search results, combining searches using history, viewing the search details.

Tools included on the Advanced Search page help users to: search for terms in a specific field, combine searches and build large, complex search strings, see how each query was translated by PubMed, and compare number of results for different queries.

Use the Advanced Search Builder to search for terms in a specific field, such as author or journal. For some fields, an autocomplete feature will provide suggestions as you type.

From the "All Fields" drop-down menu, select the field you would like to search.
Add terms from the builder to the query box to construct your search. The default Boolean operator is AND; if desired, choose OR or NOT from the pull-down menu.

You may also search a specific field -- and bypass Automatic Term Mapping -- by adding a search field tag to a term.

The Advanced Search Builder includes the Show Index feature, which provides an alphabetical display of terms appearing in selected PubMed search fields. You can browse by all fields or within specific fields such as MeSH Terms.

Click Advanced to navigate to the Advanced Search page, and use the Builder to select a search field from the All Fields menu. Note: Show Index is not available for every search field. The Show Index link will only display for fields that are compatible with this feature.
Enter a term in the search box, then click Show Index.
The index displays an alphabetic list of search terms and the approximate number of citations for each term (the actual citation count is returned when the search is executed).
Scroll until you find a term you want to include in your search, and then highlight it to add it to the search box.
Multiple terms may be selected from the list and added to the search box.
Add terms from the builder to the query box to construct your search.

More information about using the index:

PubMed processes all Boolean operators left to right.
The builder will automatically OR (and add parentheses) for multiple terms selected from the index.
A slash will display after a space. For example, the MeSH Term and Subheading "zika virus/analysis" will display after "zika virus infection/virology." Enter MeSH terms followed by a slash to go directly to the display for the MeSH/Subheading combination counts in the index.
Show Index is not available for date fields.

Your PubMed search history appears on the Advanced Search page under History. This feature requires your web browser to accept cookies.

Descriptions of each column in the History table appear below:

Search numbers may be used in place of the search string itself when combining queries (e.g., #1 OR #2).
A repeated query will move to the top of History but will retain its original numbering.
History is limited to the last 100 searches. Once the maximum number is reached, PubMed will remove the oldest search from history and add the most current search.
Actions: Add, delete, or save a query. Adding queries from History places the search string into the Query box to be used in the next search. Deleting a query removes it from History.
Query: This column shows previous search strings as entered by the user.
Details: PubMed may modify or add search terms to a search to optimize retrieval, e.g., using automatic term mapping. Click the chevron icon " > " to expand search details and see how the search was translated.
Results: The total number of citations retrieved for that query. Click the number to run the search and see the results in PubMed.
Time: Timestamp of when the search was conducted.
Please note, Microsoft Excel is typically unable to display or print more than a maximum of 1024 characters in a cell; therefore, you may want to open the CSV file with a text editor to display your complete searches.
Delete: Click "Delete" to remove all queries from History; otherwise, History expires after 8 hours of inactivity.
Click Advanced to navigate to the Advanced Search page.
Use the builder to add search terms to the query box, or type your search directly into the query box.
Use the split button to toggle the button function from "Search" to "Add to History".
Click Add to History. This will run the search without leaving the Advanced Search page.
See your query including the number of results in the History table.

Searches can be combined or used in later searches using your search History.

In the History table, click the More Actions icon " ... " next to your query.
From the available options, select "Add query" to copy the query to the Query box.
After you've added content to the Query box, options to use the Boolean operators AND, OR, or NOT will appear when adding more queries to the Query box.
Edit your query in the Query box if you would like to make any changes before running the search.
Click Search (or Add to History).

More information about combining searches from your History:

Citations in the Clipboard are represented by the search number #0, which may be used in searches. For example, to limit the citations you have collected in the clipboard to English language citations, use the following search: #0 AND english [la]. This does not change or replace the Clipboard contents.

PubMed may modify or add additional search terms to your search to optimize retrieval, such as: MeSH terms, British/American spellings, singular/plural word forms, and other synonyms.

Search Details are included on the Advanced Search page under History.
Click the chevron icon " > " next to a query in History to expand the Search Details.
When expanded, the details below a query in the History table show the search strategy used to run the search.

More information about search details:

Translations show individual term mappings using PubMed's search rules and syntax. Query terms without translations will not be listed in this section; for example, exact phrases bypass Automatic Term Mapping (ATM) .
Warnings are displayed for the original query with potential errors in bold and red type, such as syntax errors, terms not found, or invalid tags. Warnings also appear as a highlighted message in PubMed when the search is run or added to History.

Other services

Clinical queries, single citation matcher, search pubmed using the mesh database, search for journal information in the nlm catalog, using the e-utilities api tools, citation matcher api, batch citation matcher, consumer health.

PubMed Clinical Queries provides specialized searches for:

COVID-19 Articles

Clinical Study Categories

Medical Genetics

Search for COVID-19 articles

The COVID-19 article filters limit retrieval to citations about the 2019 novel coronavirus. Results are displayed in a column filtered by research topic categories. See COVID-19 article filters for the filter search strategies; these may evolve over time.

To find citations using the COVID-19 article filters:

Click Clinical Queries from the PubMed homepage
Enter your search terms in the search box
Click Search
Select a Category: General, Mechanism, Transmission, Diagnosis, Treatment, Prevention, Case Report, Forecasting, or Long COVID
Preview results in the COVID-19 Articles column
To view the results in PubMed, click the "See all" link below the results preview

To use the COVID-19 article filters in a query, add the filter name to your search with the search field tag [Filter], e.g., LitCPrevention[Filter]. The available filters are:

LitCGeneral
LitCMechanism
LitCTransmission
LitCDiagnosis
LitCTreatment
LitCPrevention
LitCCaseReport
LitCForecasting
LitCLongCOVID

Search PubMed for Remdesivir with the COVID-19 General filter:

Search by clinical study category

Clinical Study Categories use a specialized search method with built-in search filters that limit retrieval to citations reporting research conducted with specific methodologies, including those that report applied clinical research. See Clinical Study Categories filters for the filter search strategies.

To find citations using the Clinical Study Categories:

Select a Category: Therapy, Diagnosis, Etiology, Prognosis, or Clinical Prediction Guides
Select a Scope: Narrow (specific search) or Broad (sensitive search)
Preview results in the Clinical Study Categories column

Medical genetics searches

The Medical Genetics filters limit retrieval to citations related to various topics in medical genetics. See Medical genetics search filters for the filter search strategies.

To use a Medical Genetics filter, add the filter name to your search with the search field tag [Filter], e.g., Genetic Testing[Filter]. The available filters are:

Differential Diagnosis
Clinical Description
Genetic Counseling
Molecular Genetics
Genetic Testing

Search PubMed for sickle cell anemia using the Genetic Counseling filter:

The Single Citation Matcher has a fill-in-the-blank form for searching for a citation when you have some bibliographic information, such as journal name, volume, or page number.

Click Single Citation Matcher on the PubMed homepage.
Enter the citation information.

More information about using the Single Citation Matcher:

The journal box includes an autocomplete feature that suggests titles as you enter a title abbreviation or full title. Titles displayed by the autocomplete menu are in ranked order based on the number of citations in PubMed.
After selecting a journal with special characters (e.g., ampersand, colon) when using the Back button to return to the Single Citation Matcher you must clear and reenter the title.
The author box also includes an autocomplete feature that suggests author names in ranked order based on the number of citations. Full author names may be searched for citations published from 2002 forward if the full author name is available in the article.
Click either the 'Only as first author' or ‘Only as last author’ check box to limit an author name to the first or last author.

MeSH (Medical Subject Headings) is the NLM controlled vocabulary thesaurus used for indexing PubMed citations.

Use the MeSH database to find MeSH terms, including Subheadings, Publication Types, Supplementary Concepts and Pharmacological Actions, and then build a PubMed search. The MeSH database can be searched by MeSH term, MeSH Entry Term, Subheading, Publication Type, Supplementary Concept, or MeSH Scope Note.

More information about the MeSH database:

An autocomplete feature is available from the search box.
Search results are displayed in relevance-ranked order, therefore, when a user’s search exactly matches a MeSH Term, that Term is displayed first.
Click the MeSH term from the Summary display or choose Full from the display format menu to view additional information and search specifications, such as Subheadings, restrict to Major MeSH Topic, or exclude terms below the term in the MeSH hierarchy.
Year Introduced is the year the term was added to MeSH. If more than one year is shown, the term was available for indexing back to the earliest year noted. Articles are indexed using the vocabulary in place at the time of indexing, therefore, the year introduced for a term and the date of publication of a citation indexed with that term may not agree.

Launch PubMed searches from the MeSH database

To build a PubMed search from MeSH:

Run a search in the MeSH database .
Select terms using the check boxes.
Click "Add to search builder" in the PubMed search builder portlet.
You may continue searching and including additional terms to the PubMed search builder using the "Add to search builder" and Boolean pull-down menu.
When you are finished, click "Search PubMed."

The NLM Catalog includes information about the journals in PubMed and the other NCBI databases.

Click Journals in NCBI Databases on the homepage of NLM Catalog or the Journals link on the PubMed homepage to limit your NLM Catalog results to the subset of journals that are referenced in NCBI database records.

See the NLM Catalog help for additional information.

Other journal resources include:

PubMed journals with links to full text
List of all journals included in PubMed via FTP
List of Serials Indexed for Online Users

E-utilities are tools that provide access to data outside of the regular NCBI web search interface. This may be helpful for retrieving search results for use in another environment. If you are interested in large-scale data mining on PubMed data, you may download the data for free from our FTP server . Please see the terms and conditions for data users.

Fielded search

Heuristic search, auto search, rate control.

The PubMed Citation Matcher API finds PubMed identifiers (PMIDs) for citation data in structured or raw form. The interface supports three retrieval methods:

field - runs a fielded search using core bibliographic information, such as journal, date, or volume.
heuristic - collects all input elements into a single string and returns the closest matching documents.
auto - combines the two above methods and switches to heuristic mode if the fielded search has not yielded a result. This is the default method.

More information about the Citation Matcher API:

The API supports both GET and POST requests.
Data is exchanged in JSON.
Input data should be UTF-8 encoded.
The API returns a maximum of 20 PMIDs; queries returning more than 20 PMIDs are treated as bad requests.

The API root is:

method=field runs a fielded search using core bibliographic information, such as journal, date, or volume. This functionality is similar to E-utilities ESearch ; users should select the API that best suits their needs.

For a structured search, the following fields can be used:

journal - the name of the journal
pdat - the publication date, in the format YYYY/MM/DD
volume - the volume of the publication
issue - the volume of the publication
authors - one or more author names, in the format "Surname Initial" (Doe J). Optionally, the position may be specified as first, last, or auto.

Example fielded search:

GET request URL:

POST request data:

method=heuristic collects all input elements into a single string and returns the closest matching documents. It is sufficient to supply a raw citation string, such as: "The role of drag in insect hovering. J. Exp. Biol. 2004;207:4147–4155."

Example heuristic search:

method=auto first runs a fielded search , and if no results are found, it combines the fields and runs a heuristic search . This is the default method.

Example auto search:

First, a fielded search is run but no results are found due to the specified author not appearing on the citation:

Then it concatenates the fields and runs a heuristic search, which returns the closest matching document(s):

When using the PubMed Citation Matcher API programmatically, we request that you limit your application's rate to 3 requests / sec and do not make concurrent requests to this service, even at off-peak times. Additionally, requests must contain the name of the calling project in the User-Agent HTTP header value; e.g. Hydra/1.3.15 .

Use the Batch Citation Matcher to retrieve PMIDs for multiple citations. The Batch Citation Matcher requires that you enter the bibliographic information (journal, volume, page, etc.) in a specific format.

To retrieve PubMed PMIDs:

Create citation strings for the items you would like to retrieve using the following format: journal_title|year|volume|first_page|author_name|your_key| Fields must be separated by a vertical bar with a final bar at the end of the string.
Enter your email address. Email messages may take several minutes to process and be sent to your email address.
Upload your citation strings as a text file (.txt) or enter each citation string on a separate line in the text box. If citation strings are entered in the text box and a file is uploaded, the results will be an aggregate of both.
Click search.

If a match is not found the citation string will display one of the following:

your_key|NOT_FOUND;INVALID_JOURNAL - The journal name is not valid. See the journal lists or the NLM Catalog to find the correct journal abbreviation.
NOT_FOUND - The journal name is valid, but the citation string did not find a match.
AMBIGUOUS - The information provided matches more than one citation. Citation information with 3 or fewer matches include the PMIDs, and more than 3 matches include the total PMID match count. Use the Single Citation Matcher or ESearch to retrieve all citations for searched fields.
Text (.txt) format must be used when uploading a file.
You may receive multiple emails for searches containing more than 2,000 citation strings.
Enter author names without punctuation as smith jc. Initials are optional.
Your key is any string you choose to tag the citation, it is returned unaltered.
The journal title field may include the full journal title or the NLM title abbreviation.
Each citation field is searched starting with the journal title until a unique match is found.
The journal title is a required field however you may omit other fields. If you omit fields you must retain the vertical bars in the citation string. For example, if you omit the volume number 88 from the first example below it should be entered as: proc natl acad sci u s a|1991||3248|mann bj|P32022-1|

Example input:

proc natl acad sci u s a|1991|88|3248|mann bj|P32022-1|
proc natl acad sci u s a|1992|89|3271|gould se|P26261-1|
proc natl acad sci u s a|1970|89|3271|smith|P26261-1|
res microbiol|1992|143|467|ivey dm|P25966-1|
science|1987|235|182|palmenberg ac|P12296-2|
eschatology|1993|12|22|public jq|C12233-2|
virology|1993|193|492|hardy me|Q02945-1|
virus genes|1992|6|393||P27423-1|
yeast|1992|8|253|sasnauskas k|P24813-1|

Example output:

proc natl acad sci u s a|1991|88|3248|mann bj|P32022-1|2014248
proc natl acad sci u s a|1992|89|3271|gould se|P26261-1|1565618
proc natl acad sci u s a|1970|89|3271|smith|P26261-1|NOT_FOUND
res microbiol|1992|143|467|ivey dm|P25966-1|1448623
science|1987|235|182|palmenberg ac|P12296-2|3026048
C12233-2|NOT_FOUND;INVALID_JOURNAL
virology|1993|193|492|hardy me|Q02945-1|8382410
virus genes|1992|6|393||P27423-1|1335631
yeast|1992|8|253|sasnauskas k|P24813-1|1514324

The National Library of Medicine cannot provide specific medical advice. NLM urges you to consult a qualified health care professional for answers to your medical questions. NLM does not have pamphlets or other materials to mail.

MedlinePlus and MedlinePlus en español are specifically designed for consumers, containing hundreds of topic pages including NIH-written descriptive information, videos, health check tools, drug, herb and supplement info, links to Fact Sheets from other NIH Institutes, the CDC, etc., and more.

Further assistance and training

How pubmed works: automatic term mapping (atm), algorithm for finding best matching citations in pubmed, pubmed coverage, pubmed format, pubmed data field descriptions, nlm author indexing policy, error messages, mesh subheadings, pubmed character conversions, publication types, status subsets, filter search strategies, clinical queries filters, computation of similar articles, journal lists, contact customer support.

E-mail the PubMed Help Desk
Call the NLM Customer service desk: 1-888-FIND-NLM (1-888-346-3656)

Other NLM publications

PubMed Online Training
PubMed Trainer's Toolkit
NLM Technical Bulletin

Untagged terms that are entered in the search box are matched (in this order) against a Subject translation table (including MeSH (Medical Subject Headings) ), a Journals translation table, the Author index, and an Investigator (Collaborator) index.

When a match is found for a term or phrase in a translation table the mapping process is complete and does not continue on to the next translation table.

To see how your terms were translated, check the Search Details available on the Advanced Search page for each query under History. If you want to report a translation that does not seem accurate for your search topic, please e-mail the information to the NLM Help Desk .

1. Subject translation table

The Subject Translation Table contains:

British and American spellings
Pairs: singular and plural word forms, synonyms, and other closely related terms
Drug brand name to generic name translations
The See-Reference mappings (also known as entry terms) for MeSH terms
Pharmacologic action terms
Terms derived from the Unified Medical Language System (UMLS) that have equivalent synonyms or lexical variants in English
Supplementary concept (substance) names and their synonyms.

If a match is found in this translation table, the term will be searched as MeSH (that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy), and in all fields.

For example, if you enter child rearing in the search box, PubMed will translate this search to: "child rearing"[MeSH Terms] OR ("child"[All Fields] AND "rearing"[All Fields]) OR "child rearing"[All Fields]

If you enter a MeSH Term that is also a Pharmacologic Action PubMed will search the term as [MeSH Terms], [Pharmacologic Action], and [All Fields].

If you enter an entry term for a MeSH term the translation will also include an all fields search for the MeSH term associated with the entry term. For example, a search for odontalgia will translate to: "toothache"[MeSH Terms] OR "toothache"[All Fields] OR "odontalgia"[All Fields] OR "odontalgias"[All Fields] because Odontalgia is an entry term for the MeSH term toothache.

Substance name mappings do not include a mapping for individual terms in a phrase, e.g., IL-22 will not include IL[All Fields] AND 22[All Fields].

MeSH term mappings that include a standalone number or single character do not include a mapping for individual terms in a phrase, e.g., Protein C will not include Protein[All Fields] or C[All Fields].

2. Journals translation table

The Journals translation table contains the:

full journal title
title abbreviation
ISSN and eISSN number.

These will automatically map to the journal abbreviation that is used to search journals in PubMed and in all fields. For example, a search for endocrine pathology will translate to: "Endocr Pathol"[Journal] OR ("endocrine"[All Fields] AND "pathology"[All Fields]) OR "endocrine pathology"[All Fields]

3. Author index

If the term is not found in the above tables, and is not a single term, PubMed checks the author index for a match. The author index includes author names and initials, as well as full author names for articles published from 2002 forward, if available.

PubMed automatically truncates a search for an author's name to account for varying initials, e.g., o'brien j retrieves o'brien ja, o'brien jb, o'brien jc jr, as well as o'brien j.
When combining multiple authors, to avoid a match with full author names, include initials or use the [au] search tag, e.g., ryan[au] james[au]. Author names comprised of only stopwords, e.g., as a, are not searched as authors if they are part of phrase, chemical burn as a danger, unless the search only includes the author name, e.g., as a.
Initials and suffixes are not required, if you include a middle initial or suffix, you will only retrieve citations for articles that were published using the middle initial or suffix.
To distinguish author initials that may match a full author name use the [fau] search tag, e.g., peterson do[fau].

4. Investigator (Collaborator) index

If the term is not found in the above tables, except for Author, and is not a single term, the investigator index is consulted for a match. The investigator (collaborator) index includes full names, if available. Enter a full investigator name in natural or inverted order, e.g., harry janes or janes harry.

5. If no match is found?

PubMed breaks apart the phrase and repeats the above automatic term mapping process until a match is found. PubMed ignores stopwords in searches.

If there is no match, the individual terms will be combined (ANDed) together and searched in all fields.

When a search includes terms that were tagged with a search field during the automatic term mapping process and retrieves zero results, the system triggers a subsequent search using "Schema: all ." "Schema: all" modifies the search by removing the automatically added search field tags, and then searches each term in all fields.

The learned ranking algorithm combines over 150 signals that are helpful for finding best matching results. Most of these signals are computed from the query-document term pairs (e.g., number of term matches between the query and the document) while others are either specific to a document (e.g., publication type; publication year) or query (e.g., query length). The new ranking model was built on relevance data extracted from the anonymous and aggregated PubMed search logs over an extended period of time.

For more information about the Best Match algorithm, please see:

Technical details in the paper Best Match: New relevance search for PubMed by Fiorini N, Canese K, Starchenko G, et al. in PLoS Biol (2018).
NLM Technical Bulletin article: Updated Algorithm for the PubMed Best Match Sort Order

The PubMed database contains citations and abstracts to biomedical literature, facilitating searching across several NLM literature resources:

PubMed Central (PMC)

Ncbi bookshelf.

For additional information, please see the NLM Fact Sheet: Medline, PubMed, and PMC (PubMed Central): How are they different?

PubMed includes citations to original research articles, literature reviews, case reports, letters, editorials, commentaries, and other selected publications on scientific and medical topics (see: publication types found in PubMed ). Some categories of content are out of scope for PubMed, such as: book reviews, individual conference abstracts, obituaries and in memoriam articles , news and announcements, and brief summaries of research articles. More examples are included in XML Help for PubMed Data Providers: What types of articles are accepted? .

MEDLINE contains citations to journal articles in the life sciences with a concentration on biomedicine. The MEDLINE database contains citations from the late 1940s to the present , with some older material.

New citations from MEDLINE journals are received electronically from publishers and appear in PubMed daily. Most citations progress to in-process, and then to indexed for MEDLINE; however, not all citations will be indexed for MEDLINE. PubMed includes some citations from MEDLINE journals that are not indexed for MEDLINE, such as:

Citations preceding the date that a journal was selected for MEDLINE indexing.
Out-of-scope citations (e.g., articles on plate tectonics or astrophysics) from certain MEDLINE journals, primarily general science and chemistry journals, for which the life sciences articles are indexed for MEDLINE.

Citations that have been indexed for MEDLINE and updated with NLM Medical Subject Headings (MeSH) , publication types, GenBank accession numbers, and other indexing data are available daily. To limit your search to MEDLINE citations, add medline[sb] to your search.

Indexing method

The method used to assign Medical Subject Headings (MeSH) has changed over time. For more information, please see Incorporating Values for Indexing Method in MEDLINE/PubMed XML . Use the following searches to find citations indexed with each method:

Automated - MeSH indexing is provided algorithmically. Search: indexingmethod_automated
Curated - MeSH indexing is provided algorithmically and a human reviewed (and possibly modified) the algorithm results. Search: indexingmethod_curated
Fully human indexed – Search: medline[sb] NOT (indexingmethod_curated OR indexingmethod_automated)

PubMed Central (PMC) is a full text archive that includes articles from journals reviewed and selected by NLM for archiving (current and historical), as well as individual articles and preprints collected for archiving in compliance with funder policies. Some PMC content is not cited in PubMed, such as book reviews and conference abstracts (see: PubMed coverage ).

As of June 2020, PubMed Central (PMC) includes preprints that report NIH-funded research results. Citations to these preprints are deposited in PubMed. To learn more, see: NIH Preprint Pilot .

To search for preprints in PubMed, include preprint[filter] in your query.

To exclude preprints from your search results in PubMed, use the Boolean operator NOT.

Bookshelf is a full text archive of books, reports, databases, and other documents related to biomedical, health, and life sciences. PubMed includes citations for books and some individual chapters available on Bookshelf.

The PubMed Format tags table defines the data tags that compose the PubMed format. The tags are presented in alphabetical order. Some of the tags (e.g., CIN) are not mandatory and therefore will not be found in every record. Other tags (e.g., AU, MH, and RN) may occur multiple times in one record. You can download records in PubMed format as a text file (.txt) or as an .nbib file for exporting into citation management software programs .

Not all fields are searchable in PubMed. See Search field tags for the list of searchable fields.

This documentation describes the fields found in PubMed records. If a field is searchable, the search tag appears after the field name in square brackets: Affiliation [ad]. A small number of searchable fields do not correspond to a specific field in the PubMed format .

See Search field tags for a list of searchable fields.
See PubMed format for a quick table view of the fields found in PubMed records.

Affiliation may be included for authors, corporate authors and investigators, e.g., cleveland [ad] AND clinic [ad], if submitted by the publisher.

Multiple affiliations were added to citations starting from 2014, previously only the first author’s affiliation was included. PubMed includes the note "Contributed equally" in the affiliation field when this information is supplied by publishers.

Searching for terms in the affiliation field searches in all author affiliations on a citation. For example, a search for Hopkins[ad] AND Bloomberg[ad] can find these terms spread across multiple authors’ affiliations on the same citation.

To search for multiple terms appearing within the same affiliation, use a proximity search . You can also search affiliations using a phrase search ; however, we suggest using a proximity search for more comprehensive results because affiliation data may be provided in a variety of ways for the same institution.

Use proximity searching to find citations with authors from the Johns Hopkins Bloomberg School of Public Health:

This search will find any citation where the words "Hopkins," "Bloomberg," and "Public" appear in the same affiliation, with no more than forty-five words between each term. Search results may include:

Johns Hopkins Bloomberg School of Public Health
Johns Hopkins University, Bloomberg School of Public Health
Bloomberg School of Public Health, Johns Hopkins University
Bloomberg Johns Hopkins University School of Public Health
...and more!

Untagged terms and terms tagged with [all] are processed using Automatic Term Mapping (ATM) . Terms that do not map are searched in all search fields except for Place of Publication, Create Date, Completion Date, Entry Date, MeSH Date, and Modification Date. Terms enclosed in double quotes or truncated will be searched in all fields and not processed using automatic term mapping. PubMed ignores stopwords .

Includes article identifiers submitted by journal publishers such as DOI (digital object identifier).

The format to search for this field is: last name followed by a space and up to the first two initials followed by a space and a suffix abbreviation, if applicable, all without periods or a comma after the last name (e.g., fauci as or o'brien jc jr). Initials and suffixes may be omitted when searching.

PubMed automatically truncates a search for an author's name to account for varying initials, e.g., o'brien j [au] will retrieve o'brien ja, o'brien jb, o'brien jc jr, as well as o'brien j. To turn off automatic truncation, enclose the author's name in double quotes and tag with [au] in brackets, e.g., "o'brien j" [au] to retrieve just o'brien j.

Searching by full author name for articles published from 2002 forward is also possible, if available. See NLM policy on author names .

The author identifier includes a unique identifier associated with an author, corporate or investigator name, if supplied by a publisher. The field includes the organization authority that established the unique identifier, such as, ORCID, ISNI, VIAF, e.g., orcid 0000-0001-5027-4446 [auid].

The book search field includes book citations, e.g., genereviews [book].

Use the following untagged searches to retrieve all book or book chapters, e.g., ataxia AND pmcbookchapter

books and chapters: pmcbook
books: pmcbooktitle
book chapters: pmcbookchapter

The above searches capture book records provided by the NCBI Bookshelf database; they exclude a small number of documents from other providers that appear in both PubMed and Bookshelf. For the most comprehensive search of records appearing in both PubMed and Bookshelf, search "pubmed books"[sb].

The data in these fields are citations to other associated journal publications, e.g., comments or errata. Often these link to the respective citation. Comments/Corrections data can be retrieved by the search term that follows each type:

Comment in: hascommentin
Comment on: hascommenton
Corrected and republished in: hascorrectedrepublishedin
Corrected and republished from: hascorrectedrepublishedfrom
Dataset use reported in: hasassociatedpublication
Dataset described in: hasassociateddataset
Erratum in: haserratumin
Erratum for: haserratumfor
Expression of concern in: hasexpressionofconcernin
Expression of concern for: hasexpressionofconcernfor
Original Report in: hasoriginalreportin
Republished in: hasrepublishedin
Republished from: hasrepublishedfrom
Retracted and republished in: hasretractedandrepublishedin
Retracted and republished from: hasretractedandrepublishedfrom
Retraction in: hasretractionin
Retraction of: hasretractionof
Summary for patients in: hassummaryforpatientsin
Update in: hasupdatein
Update of: hasupdateof

Used by NLM for internal processing. Completon Date is not included in All Fields retrieval; the [dcom] search tag is required.

The conflict of interest statement from the published article. Conflict of interest statements are available when supplied by the publisher in the citation data sent to PubMed, or when included in full text articles in PubMed Central (PMC).

To retrieve all citations that contain conflict of interest statements, use the query hascois.

Corporate author identifies the corporate or collective authorship of an article. Corporate names display exactly as they appear in the journal.

Note: Citations indexed pre-2000 and some citations indexed in 2000-2001 retain corporate authors at the end of the title field. For comprehensive searches, consider including terms and/or words searched in the title field [ti].

The date the citation record was first created in PubMed. Create Date can be helpful when checking PubMed for citations added since the last time a query was run. Create Date is not included in All Fields retrieval; the [crdt] search tag is required.

EC/RN numbers are assigned by:

The Food and Drug Administration (FDA) Substance Registration System for Unique Ingredient Identifiers (UNIIs), e.g., Y92OUS2H9B
The Enzyme Commission (EC) to designate a particular enzyme, e.g., EC 1.1.1.57
The Chemical Abstracts Service (CAS) for Registry Numbers, e.g., 2751-14-6

The EC/RN number search field includes both the Registry Number and the Related Registry Number (available in the NLM MeSH Browser).

The editor search field includes the editors for book or chapter citations.

Entry date (EDAT) is used for PubMed processing, such as “Most Recent” sort order (i.e., last in, first out).

EDAT is typically set within 24 hours of the citation’s availability in PubMed. Exceptions: As of December 15, 2008, citations added to PubMed more than twelve months after the date of publication have the EDAT set to the date of publication, except for book citations. Prior to this, the Entry Date was set to the Publication Date on citations published before September 1997. Entry Date is not included in All Fields retrieval; the [edat] search tag is required.

Note: Entry Date was called Entrez Date in the legacy PubMed system (retired in 2020).

Technical tags used by LinkOut, filters include:

loall[sb] - citations with LinkOut links in PubMed
free full text[sb] - citations that include a link to a free full text article
full text[sb] - citations that include a link to a full text article

The first personal author name in a citation.

The full author name for articles published from 2002 forward, if available. Full author searches can be entered in natural or inverted order, e.g., julia s wong or wong julia s.

The index for the article's full investigator or collaborator name, if available. Full investigator searches can be entered in natural or inverted order, e.g., harry janes or janes harry.

The Grants and funding [gr] search field (previously Grant Number) includes grant numbers, contract numbers, or other intramural research identifiers associated with a publication.

The most common type of funding information associated with a publication in PubMed are grant numbers. Data in the Grants and funding search field can consist of up to four parts:

Number contains the grant, contract, intramural project number (or both) that designates financial support by any agency of the United States Public Health Service (US PHS), any institute of the National Institutes of Health, or other organization.
Funder code contains the 2-letter grant code or funding organization acronym, for example: CA for National Cancer Institute or DDCF for Doris Duke Charitable Foundation. See Grant Number Information Found in the GR Field in MEDLINE/PubMed (Archived) for the 2-character abbreviations, PHS agency acronyms, and other US and non-US funding organizations.
Agency includes the acronym or mnemonic in the case of US PHS agencies, or full organization name. As of 2009 this includes the agency's hierarchical structure from lower to higher entity, when known. For example, NCI NIH HHS for National Cancer Institute, National Institutes of Health, U.S. Department of Health and Human Services.
Country contains the home country of the funding agency, for example: United States.

Each individual part can be searched using [gr], for example: CA101211[gr], CA[gr], NCI[gr], NIH[gr], or United States[gr].

This field can also be searched to find articles with intramural support; e.g., "intramural nih"[gr] finds all journal citations authored by intramural NIH staff.

Completeness of funding information in PubMed will vary by source.

See Grants and funding for more information about data in this field.

Names of principal investigator(s) or collaborators who contributed to the research. Search names following the author field format, for example: soller b[ir].

The ISBN for book or book chapters.

The number of the journal issue in which the article was published.

The journal search field includes the journal title abbreviation, full journal title, or ISSN/eISSN number (e.g., J Biol Chem, Journal of Biological Chemistry, 0021-9258). If a journal title contains special characters, e.g., parentheses, brackets, enter the name without these characters, e.g., enter J Hand Surg [Am] as J Hand Surg Am.

The language search field includes the language in which the article was published. Note that many non-English articles have English language abstracts. You may search using either the language or the first three characters of most languages, e.g., chi [la] retrieves the same results as chinese [la]. The most notable exception is jpn [la] for Japanese.

The last personal author name in a citation.

Location ID includes the DOI or publisher ID that serves the role of pagination to locate an online article.

The date the citation was indexed with MeSH Terms and elevated to MEDLINE for citations with an Entry Date after March 4, 2000. The MeSH Date is initially set to the Entry Date when the citation is added to PubMed. MeSH Date is not included in All Fields retrieval; the [mhda] search tag is required.

Dates must be entered using the format YYYY/MM/DD [mhda], e.g., 2000/03/15 [mhda]. The month and day are optional (e.g., 2000 [mhda] or 2000/03 [mhda]).

To enter a date range, insert a colon (:) between each date, e.g., 1999:2000 [mhda] or 2000/03:2000/04 [mhda].

A MeSH term that is one of the main topics discussed in the article denoted by an asterisk on the MeSH term or MeSH/Subheading combination, e.g., Cytokines/physiology* See MeSH Terms [mh] below.

MeSH Subheadings are used with MeSH terms to help describe more completely a particular aspect of a subject. For example, the drug therapy of asthma is displayed as asthma/drug therapy; see MeSH/Subheading Combinations in MeSH Terms [mh] below.

The MeSH Subheading field allows users to "free float" Subheadings, e.g., hypertension [mh] AND toxicity [sh].

MeSH Subheadings automatically include the more specific Subheading terms under the term in a search. To turn off this automatic feature, use the search syntax [sh:noexp], e.g., therapy [sh:noexp].

In addition, you can enter the two-letter MeSH Subheading abbreviations rather than spelling out the Subheading, e.g., dh [sh] = diet therapy [sh].

The NLM Medical Subject Headings controlled vocabulary of biomedical terms that is used to describe the subject of each journal article in MEDLINE. MeSH is updated annually to reflect changes in medicine and medical terminology. MeSH terms are arranged hierarchically by subject categories with more specific terms arranged beneath broader terms. PubMed allows you to view this hierarchy and select terms for searching in the MeSH Database.

MEDLINE articles are automatically indexed with MeSH terms using a well-refined algorithm. Applying the MeSH vocabulary ensures that articles are uniformly indexed by subject, whatever the author's words. For more information, see Frequently Asked Questions about Indexing for MEDLINE .

More information about MeSH Terms and Major MeSH Topic search fields:

To search the term only as a MeSH term, it must be tagged using the search field, e.g., [mh] for MeSH Terms or [majr] for MeSH Major Topic. A tagged term is checked against the subject translation table , and then mapped to the appropriate MeSH term(s). To turn off mapping to multiple MeSH terms, enter the tagged MeSH term in double quotes.
MeSH terms are arranged hierarchically by subject categories with more specific terms arranged beneath broader terms. MeSH terms in PubMed automatically include the more specific MeSH terms in a search. To turn off this automatic feature, use the search syntax [mh:noexp], e.g., neoplasms [mh:noexp].For more detailed information about MeSH vocabulary including the hierarchical structure, please see the MeSH homepage .
MeSH/Subheading Combinations: To directly attach MeSH Subheadings, use the format MeSH Term/Subheading, e.g., neoplasms/diet therapy. You may also use the two-letter MeSH Subheading abbreviations , e.g., neoplasms/dh. The [mh] tag is not required, however [majr] may be used, e.g., plants/genetics[majr]. Only one Subheading may be directly attached to a MeSH term. For a MeSH/Subheading combination, PubMed always includes the more specific terms arranged beneath broader terms for the MeSH term and also includes the more specific terms arranged beneath broader Subheadings . The broader Subheading, or one of its indentions, will be directly attached to the MeSH term or one of its indentions. For example, hypertension/therapy also retrieves hypertension/diet therapy; hypertension/drug therapy; hypertension, malignant/therapy; hypertension, malignant/drug therapy, and so on, as well as hypertension/therapy.
To turn off the automatic inclusion of the more specific terms, use the syntax [field:noexp], e.g., hypertension [mh:noexp], or hypertension [majr:noexp], or hypertension/therapy [mh:noexp]. The latter example turns off the more specific terms in both parts, searching for only the one Subheading therapy attached directly to only the one MeSH term hypertension.
If parentheses are embedded in a MeSH term, replace the parentheses with a space and tag with [mh] e.g., enter the MeSH term Benzo(a)pyrene as benzo a pyrene [mh].
MeSH terms can be selected for searching in the MeSH database and from the advanced search builder index.

Modification date is a completed citation’s most recent revision date. Modification Date is not included in All Fields retrieval; the [lr] search tag is required.

The NLM ID is the alpha-numeric identifier for the cited journal that was assigned by the NLM Integrated Library System LocatorPlus, e.g., 0375267 [jid].

The author keyword field (OT field) is searchable with the title/abstract [tiab], text word [tw] and other term [ot] search tags. To retrieve all citations that have keywords, use the query haskeyword. Other term data may display an asterisk to indicate a major concept; however, you cannot search other terms with a major concept tag.

The owner search field includes the acronym that identifies the organization that supplied the citation data. Search using owner + the owner acronym, e.g., ownernasa.

Enter only the first page number that the article appears on. The citation will display the full pagination of the article but this field is searchable using only the first page number.

Use this search field tag to limit retrieval to where the name is the subject of the article, e.g., varmus h[ps]. Search for personal names as subject using the author field format, e.g., varmus h[ps].

Substances known to have a particular pharmacologic action. Each pharmacologic action term index is created with the drug/substance terms known to have that effect. This includes both MeSH terms and terms for Supplementary Concept Records.

Indicates the cited journal's country of publication. Geographic place of publication regions are not searchable. In order to retrieve records for all countries in a region (e.g., North America) it is necessary to OR together the countries of interest. Note: This field is not included in all fields or text word retrieval.

Search for PMC or NIH manuscript identifiers using the appropriate prefix followed by the ID number, e.g., PMC2600426. To retrieve all NIH manuscript citations, use the query hasnihmsid.

To search for a PubMed Identifier (PMID), enter the ID with or without the search field tag [pmid]. You can search for several PMIDs by entering each number in the search box separated by a space (e.g., 17170002 16381840); PubMed will OR the PMIDs together.

PMIDs do not change over time or during processing and are never reused.

Publication date is the date that the article was published. The search field tags [dp] and [pdat] may be used interchangeably for publication date searching.

Dates or date ranges must be searched using the format yyyy/mm/dd [dp], e.g., 1998/03/06 [dp]. The month and day are optional (e.g., 1998 [dp] or 1998/03 [dp]).

To enter a date range search, insert a colon (:) between each date, e.g., 1996:1998 [dp] or 1998/01:1998/04 [dp].

Use the following format to search X days, months or years immediately preceding today’s date where X = numeric value:

"last X days"[dp]
"last X months"[dp]
"last X year"[dp]

More information about publication dates:

The time between an article’s publication and the citation’s availability in PubMed varies depending on when the publisher deposits the citation to PubMed. Because of this, searching with Create Date [crdt] (the date a citation was created in PubMed) is often more comprehensive than Publication Date [dp] when checking PubMed on a regular basis for new citations.
Journals vary in the way the publication date appears on an issue. Some journals include just the year, whereas others include the year plus month or year plus month plus day. And, some journals use the year and season (e.g., Winter 1997). The publication date in the citation is recorded as it appears in the journal.
Publication dates without a month are set to January, multiple months (e.g., Oct-Dec) are set to the first month, and dates without a day are set to the first day of the month. Dates with a season are set as: winter = January, spring = April, summer = July and fall = October.
If an article is published electronically and in print on different dates both dates are searchable and may be included on the citation prefaced with an Epub or Print label. The electronic date will not be searchable if it is later than the print date, except when range searching.
To search for electronic dates only use the search tag [EPDAT], for print dates only tag with [PPDAT].
Most journals now publish articles online on a continuous basis, as soon as they are ready for publication (after peer review and editing, etc.) instead of, or in addition to, publishing collections of articles as an "issue" on a periodic basis. When a journal deposits a citation for an "online first" article in PubMed, NLM appends the note "[Online ahead of print]" to the online publication date. The citation is updated, and the ahead of print notation removed, when the article is included in a journal issue. The lag between the "online first" and "issue" publication dates may be days, weeks, months, or more than a year. In many cases, depending on the journal, the online first version is considered to be the version of record. The "[Online ahead of print]" note in PubMed should not be taken to mean that the cited article is not the version of record.
Bookshelf citation publication dates are generated from the book’s publication date.

Describes the material presented in the article (e.g., Review, Clinical Trial, Retracted Publication, Letter). Citations may include multiple Publication Types. Use the search tag [pt] with any PubMed Publication Type , e.g., review[pt].

Publication Types are arranged hierarchically with more specific terms arranged beneath broader terms, and publication types automatically include the more specific publication types in a search. To turn off this automatic feature, use the search syntax [pt:noexp], e.g., review [pt:noexp].

Includes publisher names for Bookshelf citations.

The SI field identifies secondary source databanks and accession numbers, e.g., GenBank, GEO, PubChem, ClinicalTrials.gov , ISRCTN. The field is composed of the source followed by a slash followed by an accession number and can be searched with one or both components, e.g., genbank [si], AF001892 [si], genbank/AF001892 [si]. To retrieve all citations with an SI value, search hasdatabanklist.

The subset field is a method of restricting retrieval by subject, citation status and journal category, with the search tag [SB]. See also filters and Find related resources using LinkOut.

Includes chemical, protocol, disease or organism terms. Synonyms to the supplementary concepts will automatically map when tagged with [nm]. This field was implemented in mid-1980; however, many chemical names are searchable as MeSH terms before that date.

Includes all words and numbers in the title, abstract, other abstract, MeSH terms, MeSH Subheadings, Publication Types, Substance Names, Personal Name as Subject, Corporate Author, Secondary Source, Comment/Correction Notes, and Other Terms (see Other Term [OT] above) typically non-MeSH subject terms (keywords), including NASA Space Flight Mission, assigned by an organization other than NLM.

Words and numbers included in the title of a citation, as well as the collection title for book citations.

Words and numbers included in a citation's title, collection title, abstract, other abstract and author keywords ( Other Term [ot] field). English language abstracts are taken directly from the published article. If an article does not have a published abstract, NLM does not create one.

Words and numbers in title originally published in a non-English language, in that language. Non-Roman alphabet language titles are transliterated. Transliterated title is not included in Text Word [TW] retrieval.

The number of the journal volume in which an article is published.

NLM author indexing policy is as follows:

1966 - 1984: MEDLINE did not limit the number of authors.
1984 - 1995: The NLM limited the number of authors to 10, with "et al" as the eleventh occurrence.
1996 - 1999: The NLM increased the limit from 10 to 25. If there were more than 25 authors, the first 24 were listed, the last author was used as the 25th, and the twenty-sixth and beyond became "et al."
2000 - Present: MEDLINE does not limit the number of authors.

More information:

Beginning in mid-2005, the policy restrictions on number of author names in past years were lifted so that on an individual basis, a citation may be edited to include all author names in the published article, regardless of the limitation in effect when the citation was created.
Effective with 1992 date of publication, letters are indexed individually with authors rather than as an anonymous group.
Until 1990, NLM transliterated up to five authors' Cyrillic or Japanese names to the Roman alphabet.
Between 1990 and 2016, the first ten Cyrillic or Japanese names are transliterated. Chinese ideograms were not transliterated by NLM, but if transliterations of the authors names are available in the journal article or table of contents, they were included in the citation, even if that includes only one author in a multi-author article.
Beginning in 2016, author names are published in Roman characters in all MEDLINE journals, and NLM no longer transliterates Cyrillic or Japanese names. All author names are included as published.

System error messages

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Typographical errors

Please contact the journal publisher directly to report an error and initiate a correction to PubMed citations for content other than MeSH.

To report a MeSH error in a PubMed citation, please contact the NLM Help Desk and include the PMID number (e.g., PMID: 12345678), and an indication of the incorrect and correct information.

NLM provides data to vendors around the world. Other products and services will not necessarily immediately reflect corrections made to PubMed records. If you search through a vendor's system, please contact your vendor about their maintenance schedules.

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In the case of PubMed, cookies store information about your interactions that may be needed later to perform a function. To use these interactive features you need to enable cookies on your computer. Consult your browser's help for information on enabling cookies.

If you have problems using cookie-dependent features of PubMed, even after enabling cookies, possible reasons may include:

Cookies are blocked by your provider or institution. Check with your Internet provider and/or the system administrator at your institution to see if cookies can be accepted. Even if you have them enabled in your web browser, if they are blocked by your provider or institution (e.g., by a firewall, proxy server, etc.), cookie-dependent features of PubMed won't work.
Your computer's date and time settings are incorrect. Check your computer's time settings to ensure that they are correct.

See the MeSH Subheadings table below and scope notes and allowable categories on the NLM website.

Certain characters have special meaning in searches, others are converted to spaces.

Searches that include the following characters are translated as follows:

parentheses ( ) - used to create Boolean nesting
square brackets [ ] - search field tag qualification
ampersand & - Boolean operator AND
pipe | - Boolean operator OR
forward slash / - MeSH/Subheading combinations
colon : - designates a range operation
double quotes " - used to force a phrase search
pound sign # - designates a History search statement when immediately followed by a number, e.g., #1 AND cat
asterisk * - wildcard symbol for search term truncation, e.g., toxicol*

Characters converted to spaces in search queries:

exclamation mark !
pound sign #
dollar sign $
percentage sign %
asterisk * (if it cannot be used in a wildcard search, for example, when a term is too short)
plus symbol +
minus symbol -
semi-colon ;
angle brackets < >
equal sign =
question mark ?
backslash \
underscore _
curly brackets { }
approximately ~
single quotes '

Some characters have special meaning in MeSH fields:

forward slash /

Publication types found in PubMed are listed below. See Publication Type [PT] and MeSH Publication Types with Scope Notes for more information; however, not all MeSH Publication Types are included in PubMed.

Adaptive Clinical Trial
Autobiography
Bibliography
Case Reports
Classical Article
Clinical Conference
Clinical Study
Clinical Trial
Clinical Trial, Phase I
Clinical Trial, Phase II
Clinical Trial, Phase III
Clinical Trial, Phase IV
Clinical Trial Protocol
Clinical Trial, Veterinary
Collected Work
Comparative Study
Consensus Development Conference
Consensus Development Conference, NIH
Controlled Clinical Trial
Corrected and Republished Article
Duplicate Publication
Electronic Supplementary Materials
English Abstract
Equivalence Trial
Evaluation Study
Expression of Concern
Festschrift
Government Publication
Historical Article
Interactive Tutorial
Introductory Journal Article
Journal Article (Default value when no more descriptive PT is provided or assigned)
Legislation
Meta-Analysis
Multicenter Study
Newspaper Article
Observational Study
Observational Study, Veterinary
Patient Education Handout
Periodical Index
Personal Narrative
Practice Guideline
Pragmatic Clinical Trial
Published Erratum
Randomized Controlled Trial
Randomized Controlled Trial, Veterinary
Research Support, American Recovery and Reinvestment Act
Research Support, N.I.H., Extramural
Research Support, N.I.H., Intramural
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.
Retracted Publication
Retraction of Publication
Scientific Integrity Review
Systematic Review
Technical Report
Validation Study
Video-Audio Media

Article attribute

Most article type filters use the article type name with the publication type [pt] search field tag; for example, "multicenter study"[pt].

The Systematic Review filter uses a search strategy in addition to the publication type [pt].

The Books and Documents filter uses the following query: "pubmed books"[sb].

The article language filters use the language name with the language [la] search field tag; for example, esperanto[la].

See Other filters and more subsets .

COVID-19 article filters

The COVID-19 article filters limit retrieval to citations about the 2019 novel coronavirus; these filters may evolve over time.

The Clinical Study Categories search filters are based on the work of Haynes RB et al.

Clinical Study Categories bibliography

The Clinical Queries search strategies have been updated based on new evidence from Haynes et al. The current strategies have better performance than their predecessors . Details of methods appear in the references below.

Revised December 2011

Wilczynski NL, McKibbon KA, Haynes RB. Sensitive Clinical Queries retrieved relevant systematic reviews as well as primary studies: an analytic survey. J Clin Epidemiol. 2011 Dec;64(12):1341-9. doi: 10.1016/j.jclinepi.2011.04.007. Epub 2011 Jul 19. PMID: 21775104 .
Lokker C, Haynes RB, Wilczynski NL, McKibbon KA, Walter SD. Retrieval of diagnostic and treatment studies for clinical use through PubMed and PubMed's Clinical Queries filters. J Am Med Inform Assoc. 2011 Sep-Oct;18(5):652-9. doi: 10.1136/amiajnl-2011-000233. Epub 2011 Jun 15. PMID: 21680559 ; PMCID: PMC3168323 .
Wilczynski NL, Haynes RB; QI Hedges Team. Optimal search filters for detecting quality improvement studies in Medline. Qual Saf Health Care. 2010 Dec;19(6):e31. doi: 10.1136/qshc.2010.042432. Epub 2010 Jul 29. PMID: 20671080 .
Kastner M, Wilczynski NL, McKibbon AK, Garg AX, Haynes RB. Diagnostic test systematic reviews: bibliographic search filters ("Clinical Queries") for diagnostic accuracy studies perform well. J Clin Epidemiol. 2009 Sep;62(9):974-81. doi: 10.1016/j.jclinepi.2008.11.006. Epub 2009 Feb 20. PMID: 19230607 ; PMCID: PMC2737707 .
Wilczynski NL, Haynes RB. Response to Corrao et al.: Improving efficacy of PubMed clinical queries for retrieving scientifically strong studies on treatment. J Am Med Inform Assoc. 2007 Mar-Apr;14(2):247-8. Epub 2007 Jan 9. PMID: 17213490 ; PMCID: PMC2213472 .
Wilczynski NL, McKibbon KA, Haynes RB. Response to Glanville et al.: How to identify randomized controlled trials in MEDLINE: ten years on. J Med Libr Assoc. 2007 Apr;95(2):117-8; author reply 119-20. PMID: 17443240 ; PMCID: PMC1852612 .
Wilczynski NL, Morgan D, Haynes RB; Hedges Team. An overview of the design and methods for retrieving high-quality studies for clinical care. BMC Med Inform Decis Mak. 2005 Jun 21;5:20. doi: 10.1186/1472-6947-5-20. PMID: 15969765 ; PMCID: PMC1183213 .
Haynes RB, McKibbon KA, Wilczynski NL, Walter SD, Werre SR; Hedges Team. Optimal search strategies for retrieving scientifically strong studies of treatment from Medline: analytical survey. BMJ. 2005 May 21;330(7501):1179. doi: 10.1136/bmj.38446.498542.8F. Epub 2005 May 13. PMID: 15894554 ; PMCID: PMC558012 .
Montori VM, Wilczynski NL, Morgan D, Haynes RB; Hedges Team. Optimal search strategies for retrieving systematic reviews from Medline: analytical survey. BMJ. 2005 Jan 8;330(7482):68. doi: 10.1136/bmj.38336.804167.47. Epub 2004 Dec 24. PMID: 15619601 ; PMCID: PMC543864 .
Wilczynski NL, Haynes RB, Lavis JN, Ramkissoonsingh R, Arnold-Oatley AE; HSR Hedges team. Optimal search strategies for detecting health services research studies in MEDLINE. CMAJ. 2004 Nov 9;171(10):1179-85. doi: 10.1503/cmaj.1040512. PMID: 15534310 ; PMCID: PMC524948 .
Wilczynski NL, Haynes RB; Hedges Team. Developing optimal search strategies for detecting clinically sound prognostic studies in MEDLINE: an analytic survey. BMC Med. 2004 Jun 9;2:23. doi: 10.1186/1741-7015-2-23. PMID: 15189561 ; PMCID: PMC441418 .
Haynes RB, Wilczynski NL. Optimal search strategies for retrieving scientifically strong studies of diagnosis from Medline: analytical survey. BMJ. 2004 May 1;328(7447):1040. doi: 10.1136/bmj.38068.557998.EE. Epub 2004 Apr 8. PMID: 15073027 ; PMCID: PMC403841 .
Bhandari M, Montori VM, Devereaux PJ, Wilczynski NL, Morgan D, Haynes RB; Hedges Team. Doubling the impact: publication of systematic review articles in orthopaedic journals. J Bone Joint Surg Am. 2004 May;86(5):1012-6. PMID: 15118046 .
Wong SS, Wilczynski NL, Haynes RB; Hedges Team. Developing optimal search strategies for detecting clinically relevant qualitative studies in MEDLINE. Stud Health Technol Inform. 2004;107(Pt 1):311-6. PMID: 15360825 .
Montori VM, Wilczynski NL, Morgan D, Haynes RB; Hedges Team. Systematic reviews: a cross-sectional study of location and citation counts. BMC Med. 2003 Nov 24;1:2. doi: 10.1186/1741-7015-1-2. PMID: 14633274 ; PMCID: PMC281591 .
Wong SS, Wilczynski NL, Haynes RB, Ramkissoonsingh R; Hedges Team. Developing optimal search strategies for detecting sound clinical prediction studies in MEDLINE. AMIA Annu Symp Proc. 2003;2003:728-32. PMID: 14728269 ; PMCID: PMC1479983 .
Wilczynski NL, Haynes RB; Hedges Team. Developing optimal search strategies for detecting clinically sound causation studies in MEDLINE. AMIA Annu Symp Proc. 2003;2003:719-23. PMID: 14728267 ; PMCID: PMC1480286 .
Wilczynski NL, McKibbon KA, Haynes RB. Enhancing retrieval of best evidence for health care from bibliographic databases: calibration of the hand search of the literature. Stud Health Technol Inform. 2001;84(Pt 1):390-3. PMID: 11604770 .
Haynes RB, Wilczynski N, McKibbon KA, Walker CJ, Sinclair JC. Developing optimal search strategies for detecting clinically sound studies in MEDLINE. J Am Med Inform Assoc. 1994 Nov-Dec;1(6):447-58. doi: 10.1136/jamia.1994.95153434. PMID: 7850570 ; PMCID: PMC116228 .

Medical genetics search filters

The medical genetics searches were developed in conjunction with the staff of GeneReviews: Genetic Disease Online Reviews at GeneTests, University of Washington, Seattle.

The neighbors of a document are those documents in the database that are the most similar to it. The similarity between documents is measured by the words they have in common, with some adjustment for document lengths. To carry out such a program, one must first define what a word is. For us, a word is basically an unbroken string of letters and numerals with at least one letter of the alphabet in it. Words end at hyphens, spaces, new lines, and punctuation. The 132 common, but uninformative, words (also known as stopwords) are eliminated from processing at this stage. Next, a limited amount of stemming of words is done, but no thesaurus is used in processing. Words from the abstract of a document are classified as text words. Words from titles are also classified as text words, but words from titles are added in a second time to give them a small advantage in the local weighting scheme. MeSH terms are placed in a third category, and a MeSH term with a subheading qualifier is entered twice, once without the qualifier and once with it. If a MeSH term is starred (indicating a major concept in a document), the star is ignored. These three categories of words (or phrases in the case of MeSH) comprise the representation of a document. No other fields, such as Author or Journal, enter into the calculations.

Having obtained the set of terms that represent each document, the next step is to recognize that not all words are of equal value. Each time a word is used, it is assigned a numerical weight. This numerical weight is based on information that the computer can obtain by automatic processing. Automatic processing is important because the number of different terms that have to be assigned weights is close to two million for this system. The weight or value of a term is dependent on three types of information: 1) the number of different documents in the database that contain the term; 2) the number of times the term occurs in a particular document; and 3) the number of term occurrences in the document. The first of these pieces of information is used to produce a number called the global weight of the term. The global weight is used in weighting the term throughout the database. The second and third pieces of information pertain only to a particular document and are used to produce a number called the local weight of the term in that specific document. When a word occurs in two documents, its weight is computed as the product of the global weight times the two local weights (one pertaining to each of the documents).

The global weight of a term is greater for the less frequent terms. This is reasonable because the presence of a term that occurred in most of the documents would really tell one very little about a document. On the other hand, a term that occurred in only 100 documents of one million would be very helpful in limiting the set of documents of interest. A word that occurred in only 10 documents is likely to be even more informative and will receive an even higher weight.

The local weight of a term is the measure of its importance in a particular document. Generally, the more frequent a term is within a document, the more important it is in representing the content of that document. However, this relationship is saturating, i.e., as the frequency continues to go up, the importance of the word increases less rapidly and finally comes to a finite limit. In addition, we do not want a longer document to be considered more important just because it is longer; therefore, a length correction is applied. This local weight computation is based on the Poisson distribution and the formula can be found in Lin J and Wilbur WJ .

The similarity between two documents is computed by adding up the weights (local wt1 × local wt2 × global wt) of all of the terms the two documents have in common. This provides an indication of how related two documents are. The resultant score is an example of a vector score. Vector scoring was originated by Gerard Salton and has a long history in text retrieval. The interested reader is referred to Salton, Automatic Text Processing, Reading, MA: Addison-Wesley, 1989 for further information on this topic. Our approach differs from other approaches in the way we calculate the local weights for the individual terms. Once the similarity score of a document in relation to each of the other documents in the database has been computed, that document's neighbors are identified as the most similar (highest scoring) documents found. These closely related documents are pre-computed for each document in PubMed so that when you select Similar articles, the system has only to retrieve this list. This enables a fast response time for such queries.

PubMed journals

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UNIX Compress

PubMed and NCBI molecular biology database journals

NCBI Literature Resources

MeSH PMC Bookshelf Disclaimer

The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). Unauthorized use of these marks is strictly prohibited.

PubMed: Find Research Articles

Run a Search
Find Full Text
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Export to Citation Managers
New PubMed Essentials

Finding Comparative Effectiveness Research

Comparative effectiveness research is the conduct and synthesis of research comparing the benefits and harms of different interventions and strategies to prevent, diagnose, treat and monitor health conditions in "real world" settings.

Two specialized resources are available to inform comparative effectiveness research:

Comparative Effectiveness Research on the PubMed Topic-Specific Queries page. Provides specialized PubMed searches of published research and research in progress to help inform investigations of comparative effectiveness.

Medline Plus is the world’s largest medical library, it brings you information about diseases, conditions, and wellness issues in language you can understand. MedlinePlus offers reliable, up-to-date health information, anytime, anywhere, for free.

3 Ways to Find Research Articles in PubMed

1. filter (limit) to article type.

Most citations in PubMed are for journal articles. However, you may limit your retrieval based on the type of material the article represents. Use the Filters on the Results page sidebar and look at the Article Types checklist which contains a list of frequently searched publication types.

For example, choose Randomized Controlled Trial or Clinical Trial or Meta-Analysis from the list.

2. PubMed Clinical Queries

Enter your search terms and evidence-filtered citations will appear under Clinical Study Categories. Systematic Reviews or Medical Genetics. The Clinical Queries link is found on the PubMed home page or under the More Resources drop-down at the top of the Advanced Search page.

The resulting retrieval in PubMed Clinical Queries can be further refined using PubMed's Filters, e.g., English language, humans.

3. Limit to Articles with Structured Abstracts

Many abstracts that are added to PubMed include section labels such as BACKGROUND, OBJECTIVE, METHODS, RESULTS, and CONCLUSIONS. These 'structured' abstracts appear in many different article types such as review articles, original research, and practice guidelines and facilitate skimming of citations for relevance and specific information such as research design within the Methods section. The presence of structured abstracts in citations are a searchable feature in PubMed. To limit to citations containing structured abstracts, include the term hasstructuredabstract in the search box.

For example: valerian AND sleep AND hasstructuredabstract

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Last Updated: Jul 18, 2023 11:35 AM
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Filters and Narrowing Searches

Searching PubMed: Filters and Narrowing Searches

Created by health science librarians.

Basic Searches

PubMed Field Tags

Use filters to focus the search, article types, clinical queries.

Find Full-Text Articles
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Literature Reviews

You can use field tags in PubMed to limit your search to only the specified fields of the citations. For instance, you can add a title field tag and only search for a word or words in article titles. Without field tags, PubMed defaults to searching every field of a citation. This means you're searching the article title, abstract/summary, author-supplied keywords, PubMed indexing terms, and other fields like author names, authors' institutions, journal names, etc.

If your search seems to have too many irrelevant results, using field tags can help narrow your search. To use field tags, add the code in brackets immediately following the search term. For instance, to only search for dogs in the titles of articles, you'd search for dogs[TI] in PubMed.

A list of common field tags is below:

Learn more about PubMed Field Tags

Use the filter options available in the left sidebar of the search results page to focus the search.

how to find primary research articles on pubmed

Important : The "Free full text" filter does not include UNC-CH journals subscriptions. The "Full text" filter is not an accurate limit to UNC-CH journal subscriptions. Use the Find @ UNC button to find full-text articles.

Show Additional Filters

The default list of filter categories in the left hand sidebar does not include all options. Click on the link labeled "Choose additional filters" to add categories to the list. Filters are available to focus your search results by article types, text availability, publication dates, species, languages, sex, subjects, journal categories, ages, and search fields. Click on the boxes to activate the filters. For more filter options click on the additional filters option.

Type of Article, Species, Sex, and Ages filters are based on terms added by indexers. When these filters are selected they remove very recent articles that have not yet been indexed. Always look at the most recent search results before adding these filters.

Activated Filters Display on Search Result Pages. Filters stay selected during the current search session until you change or clear them.

Once the filters are selected on the above screenshot they appear as boxes on the left hand of the screen on the results page. Tick those boxes to show the changes in the search results.

Go to PubMed Help to learn more about using filters.

Research Study Filters

Add options to the "Article types" list by clicking on the "Additional Filters" link on the left of search result screen and selecting ones you want to use.

Therapy, intervention, and prevention search results can be limited to articles reporting clinical research by selecting Clinical Trial, Meta-Analysis, Randomized Control Trial or Systematic Reviews from the "Articles types" list.

You can then select the filter you want. Following that check the left hand box to have it appear in the search results.

Clinical Trial : "Work that is the report of a pre-planned clinical study of the safety, efficacy, or optimum dosage schedule of one or more diagnostic, therapeutic, or prophylactic drugs, devices, or techniques in humans."
Meta-Analysis : "Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials."
Randomized Control Trial : "Work consisting of a clinical trial that involves at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table."
Systematic Reviews --retrieves "citations identified as systematic reviews, meta-analyses, reviews of clinical trials, evidence-based medicine, consensus development conferences, guidelines, and citations to articles from journals specializing in review studies of value to clinicians." Systematic Review Filter Search Strategy

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Literature Searching

In this guide.

Introduction
Steps for searching the literature in PubMed
Step 1 - Formulate a search question
Step 2- Identify primary concepts and gather synonyms
Step 3 - Locate subject headings (MeSH)
Step 4 - Combine concepts using Boolean operators
Step 5 - Refine search terms and search in PubMed
Step 6 - Apply limits

Steps for Searching the Literature

Searching is an iterative process and often requires re-evaluation and testing by adding or changing keywords and the ways they relate to each other. To guide your search development, you can follow the search steps below. For more information on each step, navigate to its matching tab on the right menu.

1. Formulate a clear, well-defined, answerable search question

Generally, the basic literature search process begins with formulating a clear, well-defined research question. Asking the right research question is essential to creating an effective search. Your research question(s) must be well-defined and answerable. If the question is too broad, your search will yield more information than you can possibly look through.

2. Identify primary concepts and gather synonyms

Your research question will also help identify the primary search concepts. This will allow you to think about how you want the concepts to relate to each other. Since different authors use different terminology to refer to the same concept, you will need to gather synonyms and all the ways authors might express them. However, it is important to balance the terms so that the synonyms do not go beyond the scope of how you've defined them.

3. Locate subject headings (MeSH)

Subject databases like PubMed use 'controlled vocabularies' made up of subject headings that are preassigned to indexed articles that share a similar topic. These subject headings are organized hierarchically within a family tree of broader and narrower concepts. In PubMed and MEDLINE, the subject headings are called Medical Subject Headings (MeSH). By including MeSH terms in your search, you will not have to think about word variations, word endings, plural or singular forms, or synonyms. Some topics or concepts may even have more than one appropriate MeSH term. There are also times when a topic or concept may not have a MeSH term.

4. Combine concepts using Boolean operators AND/OR

Once you have identified your search concepts, synonyms, and MeSH terms, you'll need to put them together using nesting and Boolean operators (e.g. AND, OR, NOT). Nesting uses parentheses to put search terms into groups. Boolean operators are used to combine similar and different concepts into one query.

5. Refine search terms and search in PubMed

There are various database search tactics you can use, such as field tags to limit the search to certain fields, quotation marks for phrase searching, and proximity operators to search a number of spaces between terms to refine your search terms. The constructed search string is ready to be pasted into PubMed.

6. Apply limits (optional)

If you're getting too many results, you can further refine your search results by using limits on the left box of the results page. Limits allow you to narrow your search by a number of facets such as year, journal name, article type, language, age, etc.

Depending on the nature of the literature review, the complexity and comprehensiveness of the search strategies and the choice of databases can be different. Please contact the Lane Librarians if you have any questions.

The type of information you gather is influenced by the type of information source or database you select to search. Bibliographic databases contain references to published literature, such as journal articles, conference abstracts, books, reports, government and legal publications, and patents. Literature reviews typically synthesis indexed, peer-reviewed articles (i.e. works that generally represent the latest original research and have undergone rigorous expert screening before publication), and gray literature (i.e. materials not formally published by commercial publishers or peer-reviewed journals). PubMed offers a breadth of health sciences literature and is a good starting point to locate journal articles.

What is PubMed?

PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. Available to the public online since 1996, PubMed was developed and is maintained by the National Center for Biotechnology Information (NCBI) , at the U.S. National Library of Medicine (NLM) , located at the National Institutes of Health (NIH) .

MEDLINE is the National Library of Medicine’s (NLM) premier bibliographic database that contains more than 27 million references to journal articles from more than 5,200 worldwide journals in life sciences with a concentration on biomedicine. The Literature Selection Technica Review Committee (LSTRC) reviews and selects journals for MEDLINE based on the research quality and impact of the journals. A distinctive feature of MEDLINE is that the records are indexed with NLM Medical Subject Headings (MeSH).

PubMed also contains citations for PubMed Central (PMC) articles. PMC is a full-text archive that includes articles from journals reviewed and selected by NLM for archiving (current and historical), as well as individual articles collected for archiving in compliance with funder policies. PubMed allows users to search keywords in the bibliographic data, but not the full text of the PMC articles.

How to Access PubMed?

To access PubMed, go to the Lane Library homepage and click PubMed in "Top Resources" on the left. This PubMed link is coded with Find Fulltext @ Lane Library Stanford that links you to Lane's full-text articles online.

<< Previous: Introduction
Next: Step 1 - Formulate a search question >>
Last Updated: Jan 9, 2024 10:30 AM
URL: https://laneguides.stanford.edu/LitSearch

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The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

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PubMed Central ® (PMC) is a free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health's National Library of Medicine (NIH/NLM)

Discover a digital archive of scholarly articles, spanning centuries of scientific research.

Learn how to find and read articles of interest to you.

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Browse the PMC Journal List or learn about some of PMC's unique collections.

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Navigate the PMC submission methods to comply with a funder mandate, expand access, and ensure preservation.

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Learn about deposit options for journals and publishers and the PMC selection process.

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Find tools for bulk download, text mining, and other machine analysis.

9.8 MILLION articles are archived in PMC.

Content provided in part by:, full participation journals.

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Journals deposit all NIH-funded articles as defined by the NIH Public Access Policy.

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Publisher deposits a subset of articles from a collection of journals.

March 21, 2024

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We are pleased to announce the availability of a preview of improvements planned for the PMC website. These…

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The PubReader format was added to PMC in 2012 to make it easier to read full text articles on tablet, mobile, and oth…

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Pubmed: searching tips & more: home, accessing pubmed.

Direct link to this guide: guides.lib.berkeley.edu/pubmed .

This PubMed exercise set (docx) will help get you started using PubMed's search features, including filters, field tags, MeSH, and more.

The PubMed FAQ and User Guide is your best bet for up-to-date PubMed help.

PubMed Searching: Top Tips; Details Below

Combine terms with AND or OR ;
Use Filters (eg, Ages, Article types, Languages, etc.);
Search for your term as a word in the title or title or abstract (using Filters, Advanced Search, or Field Tags );
Use MeSH (Medical Subject Headings), with subheadings ;
Use the Similar articles link located by each citation;
Always keep in mind the question you are trying to answer when creating a search strategy and when reviewing the articles you find .

Search Tips

Looking for a known article? In the Search box, simply type the article title, or a combination of article title words with author and/or journal name words, and click Search. PubMed's citation sensor will automatically analyze your query for citation information to return the correct citation. More information in the PubMed User Guide .

Subject Searching : For most literature reviews, it may be best to search narrowly: think of your topic in specific concepts: Who is your population ? Are you looking at a specific outcome or intervention ? Are you interested in a specific geography ? Do you only want studies that used a particular method ? Build your search using the concepts that describe what you want, then broaden or narrow the search as needed. Consult our Searching the Public Health Literature More Effectively Guide for more literature searching tips.

Search specific fields (author name or affiliation, word in title and/or abstract, journal name, etc.) : Two methods: Field Tags or Advanced Search

Field tags exist for every field in a PubMed record. For example, type cell[ta] to search for articles in the journal Cell. Affiliation (tag is [ad]) can include any field in an author's address. Type cell[ta] AND (berkeley[ad] OR 94720[ad]) to find articles in Cell by Berkeley authors. A complete list of field tags (there are several dozen) is in the PubMed User Guide .

Click Advanced under the search box to be taken to PubMed's Advanced Search page where you can use a drop-down menu to specify fields to be searched. Click Add to add the term to the search box. You may then use the drop-down menu to add another field to be searched; click AND (or change to OR or NOT), to add it to the Query box:

pubmed advanced search builder with affiliation search indicated

More information in the PubMed User Guide

Looking for a Plain Language Summary? In the Search box, type AND hasplainlanguagesummary after your search terms. Each citation your search finds will have a plain English summary of the article. Example: asthma inhalers AND hasplainlanguagesummary .

New! Proximity Searching: Search for multiple terms appearing in any order within a specified distance of one another in the [Title] or [Title/Abstract] fields. To create a proximity search in PubMed, enter terms using the following format:

"search terms"[field:~N]

Search terms = Two or more words enclosed in double quotes.
Field = The search field tag for the [Title] or [Title/Abstract] fields.
N = The maximum number of words that may appear between your search terms.

For example, to search PubMed for citations where the terms "hip" and "pain" appear with no more than two words between them in the Title/Abstract search field, try the search:

"hip pain"[Title/Abstract:~2]

Search results may include hip pain, hip-related pain, hip joint pain, hip/groin pain, hip biomechanics and pain, pain after total hip arthroplasty, pain in right hip, and more.

See the PubMed User Guide and view the proximity searching tutorial for more examples and information about proximity searching in PubMed.

Search History

Click Advanced (under the Search box) and scroll down to see your search history . Click > in the Details column to see how PubMed translated your query. Click the number in the Results column to go back to the search results for that search. You can build new searches or revise past searches here; details in the PubMed User Guide . It is highly recommended that you download your search history by clicking the Download button. This will help you keep track of what and when you searched; this is especially important when doing a systematic review.

Exporting Citation to Reference Management Software

EndNote: Open your EndNote library. Select the PubMed citations to export by clicking in the checkbox to the left of each. Click Send to (just under the search box) and choose Citation manager , then click Create file . The first time you do this, make sure EndNote or Research Soft Direct Export is selected as the Open with program; navigate to the EndNote program on your computer if necessary. Click OK.

RefWorks (Note: UC Berkeley's access to RefWorks will end in 2024): Tools . Click Install Save to RefWorks , then drag the bookmarklet to your favorites toolbar.--> Note: Currently, RefWorks Save to RefWorks bookmarklet does not always work with PubMed. In PubMed, select the citations to export by clicking in the checkbox to the left of each. Click Save , and make sure Selection (number) is what you see on that drop-down menu. Choose PubMed in the Format menu, and then Create file . Save the file to somewhere you will remember. In RefWorks, select Add > Import references . Select a file from your computer or drag and drop it onto the import page, then click Import . You can select which RefWorks folder to import into.

Zotero: Note: Currently the Zotero Connector does not always work with PubMed. In PubMed, select the citations to export by clicking in the checkbox to the left of each. Click Save , and make sure Selection (number) is what you see on that drop-down menu. Choose PubMed in the Format menu, and then Create file . Save the file to somewhere you will remember. In Zotero, click File > Import... > A File, and navigate to the file you saved. Select it and click Open.

Mendeley: In PubMed, select the citations to export by clicking in the checkbox to the left of each. Click Save , and make sure Selection (number) is what you see on that drop-down menu. Choose PubMed in the Format menu, and then Create file . Save the file to somewhere you will remember. In Mendeley, select the folder you want to import into, and click Add Files . Select the search results file.

Others: Most citation managers will let you import a text file in RIS format . Save citations in the PubMed format , which is comparable to RIS format, then import into your citation manager.

More information in the PubMed User Guide .

PubMed's "Cite" feature: Another option: When you are viewing a record, click Cite on the right side, select the desired citation style, then click Copy . You may also click Download .nbib to download and add that single citation to your reference management software.

Using Search Filters

After running a search, use the filters on the left side to limit your search results. Click Additional filters to add filtering options such as article type, language, and age groups. Note that selected filters will "stick" for future searches until you de-select them. More information is in the PubMed User Guide .

Important note : Using filters will have the effect of limiting your search results to include only citations with MeSH terms applied; see below on what will be excluded by limiting your search to only include citations with MeSH terms.

Using MeSH (Medical Subject Headings)

Why MeSH? Using Medical Subject Headings, or MeSH , may help you retrieve more relevant search results. MeSH are the subject terms applied to nearly all PubMed citations. However, it is important to remember that some PubMed citations - including the very newest citations - do not have MeSH terms applied to them, and therefore will not appear in a search that exclusively uses MeSH terms.

Three ways to search using MeSH :

Use the MeSH terms from a known, relevant article : Search for a known article, click to open the full record, then scroll down to see the MeSH terms applied to that article. Clicking on a MeSH term will allow you to either search PubMed using only that term, or add that term to the search box; you can then add additional terms and execute your search.
Use the MeSH Database to find terms, then build a search using those terms : Step-by step instructions may be found in the PubMed User Guide (scroll down to "Launch PubMed searches from the MeSH database").
Use Advanced Search to search using known MeSH terms : If you know the MeSH terms you want to use for your search, click Advanced under the Search box, then use the drop-down menu in Advanced Search. Instructions in the PubMed User Guide .

To see suggested MeSH terms based on a block of submitted text (ie, an abstract, article, etc.), use the MeSH on Demand tool . MeSH on Demand also lists similar PubMed articles relevant to your submitted text, thus MeSH on Demand can help you find articles similar to a known, relevant article.

MeSH Subheadings (or " Qualifiers ") help focus your search results more precisely. In the MeSH Database, select desired subheadings, then click Add to search builder , then click Search PubMed :

MeSH Database showing subheadings of a MeSH term

Help & Tutorials

The PubMed User Guide is updated frequently. It includes FAQs on most common search issues, as well as search tips and more. Examples:

I retrieved too many citations. How can I focus my search?
I retrieved too few citations. How can I expand my search?
How do I find systematic reviews ?

PubMed's Online Training website includes numerous tutorials, guides, and handouts.

See also the UC Berkeley Library PubMed Quick Guide for more tips and examples.

Alternative PubMed Search Interfaces

The Medline subset of PubMed , which consists of articles assigned MeSH terms, and comprises the overwhelming majority of PubMed citations, is available for searching in both Ovid Medline and in Embase .

PubMed PubReMiner lets you enter a search, and the results will list terms in a frequency order : you will see lists of MeSH terms, title words, abstract words, authors, journals, etc., in the frequency order each of these appears in your search result. This can help you come up with additional terms to include in your search, as well as the top publishing authors and journals on your topic.

Use PubMed by Year to see a graph the number and rate per 100,000 citations of your search terms, and to compare to the frequency of various terms over time. PubMed by Year searches from the oldest citations in PubMed (1781) to the current year. Data downloadable to csv or svg.

PubVenn enables you to explore PubMed using Venn diagrams. Enter any multi-term search to see the relative size of the citation set for each term as well as how those sets interact. The resulting diagrams are printable.

Once you have a PubMed search strategy, you can use the Polyglot Search tool to translate your PubMed search into the correct syntax for several other databases, including Embase, Scopus, Web of Science, and more.

My NCBI: Customizing PubMed & More

My NCBI allows you to save searches and citations, customize PubMed, and more. Click Log in (top right of PubMed home page); you will be presented with several options. Unless you already use an eRA or NIH logon, we strongly suggest you select more login options , then start typing berkeley and choose University of California, Berkeley . You can then log in using CalNet. Once logged in, click your user name (top right) then select Dashboard (My NCBI) . Here will be your:

Saved Searches (which you can have re-run as an "alert" on a schedule);
Collections (citations you have saved, which you can share if desired);
Custom filters you have created;

and more. Detailed instructions may be found in My NCBI Help . If you already are a NCBI user, please note: As of June 2022, you will be required to login using a 3rd-party option .

Last Updated: Feb 13, 2024 11:28 AM
URL: https://guides.lib.berkeley.edu/pubmed

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Identifying Articles
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Scenarios in PubMed

Primary Research Article

Review article.

Identifying and creating an APA style citation for your bibliography:

Author initials are separated by a period
Multiple authors are separated by commas and an ampersand (&)
Title format rules change depending on what is referenced
Double check them for accuracy

Identifying and creating an APA style in-text citation:

eg. (Smith, 2022) or (Smith & Stevens, 2022)

The structure of this changes depending on whether a direct quote or parenthetical used:

Direct Quote: the citation must follow the quote directly and contain a page number after the date

eg. (Smith, 2022, p.21)

Parenthetical: the page number is not needed

For more information, take a look at Harvard Library's Citation Styles guide !

A primary research article typically contains the following section headings:

"Methods"/"Materials and Methods"/"Experimental Methods"(different journals title this section in different ways)

"Results"

"Discussion"

If you skim the article, you should find additional evidence that an experiment was conducted by the authors themselves.

Primary research articles provide a background on their subject by summarizing previously conducted research, this typically occurs only in the Introduction section of the article.

Review articles do not report new experiments. Rather, they attempt to provide a thorough review of a specific subject by assessing either all or the best available scholarly literature on that topic.

Ways to identify a review article:

Author(s) summarize and analyze previously published research
May focus on a specific research question, comparing and contrasting previously published research
Overview all of the research on a particular topic
Does not contain "methods" or "results" type sections
<< Previous: Scenarios in PubMed
Last Updated: Oct 3, 2023 4:16 PM
URL: https://guides.library.harvard.edu/PubMed

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Finding Primary Articles in PubMed: Home

APA Citations

Finding Primary Articles in PubMed

From the library homepage -- library.surry.edu (opens in new window) -- click on Find Articles .

Click on the letter P or scroll through the list until you see PubMed . To limit to full text articles, click on the PubMed Central link in the PubMed description.

Type in a search for your topic. Press Enter or click the Search button.

You will retrieve a list of articles. To limit to primary research articles, click on Clinical Trial or click More to select other type of trials and original research studies.

You may also limit your article results to Free full text either on the left or you can scan below the article results for Free Article or Free PMC Article .

If the article is available for free, you will see a link to access the article in the upper right of the screen. If you can't find the article text, email Alan Unsworth, Research Librarian , to see if the article may be obtained .

Next: APA Citations >>
Last Updated: Nov 9, 2023 2:07 PM
URL: https://library.surry.edu/pubmed

Finding Primary Research Articles in the Sciences: Home

Advanced Search-Databases
Primary vs. Secondary
Analyzing a Primary Research Article
MLA, APA, and Chicago Style

This guide goes over how to find and analyze primary research articles in the sciences (e.g. nutrition, health sciences and nursing, biology, chemistry, physics, sociology, psychology). In addition, the guide explains how to tell the difference between a primary source and a secondary source in scientific subject areas.

If you are looking for how to find primary sources in the humanities and social sciences, such as direct experience accounts in newspapers, diaries, artwork and so forth, please see Finding Primary Sources in the Humanities and Social Sciences .

Recommended Databases

To get started, choose one of the databases below. Once you log in, enter your search terms to start looking for primary articles.

Link to all Polk State College Library databases

Login Required

You must log in to use library databases and eBooks. When prompted to log in, enter your Passport credentials.

If you have trouble, try resetting your Passport pin , sending an email to [email protected] , or calling the Help Desk at 863.292.3652 .

You can also get help from Ask a Librarian .

Search Tips

Keep your search terms simple.

No need to type full sentences into the database search box. Limit your search to 2-3 words.
There is no need to type "research article" into the search box.

Use the "Advanced Search" feature of the database.

This will allow you to limit your search to only peer reviewed articles or a certain time frame (for example: 2013 or later).
Click the red tab above for tips on advanced search strategies .

Re-read the assignment guidelines often

Does this article satisfy the scope of the assignment (e.g. a study focused on nutrition)?
Does it meet the criteria for the assignment (e.g. an original research article)?

Not finding what you are looking for?

Ask a Librarian!

Search and Find a Primary Research Article

Are you looking for a primary research journal article if so, that is an article that reports on the results of an original research study conducted by the authors themselves. .

You can use the library's databases to search for primary research articles. A research article will almost always be published in a peer-reviewed journal. Therefore, it is a good idea to limit your results to peer-reviewed articles. Click on the Advanced Search-Databases tab at the top of this guide for instructions.

The following is _not_ primary research:

Review articles are studies that arrive at conclusions after looking over other studies. Therefore, review articles are not primary (think "first") research. There are a variety of review articles, including:

Literature Reviews
Systematic Reviews
Meta-Analyses
Scoping Reviews
Topical Reviews
A review/assessment of the evidence

Having trouble? Look for a method section within the article. If the method section includes the process used to conduct the research, how the data was gathered and analyzed and any limitations or ethical concerns to the study, then it is most likely a primary research article. For example: a research article will describe the number of people (e.g. 175 adults with celiac disease) who participated in the study and who were used to collect data.

If the method section describes how the authors found articles on a topic using search terms or databases , then it is mostly likely a secondary review article and not primary research. If there is no method section, it is not a primary research article.

Other sections in a journal:

Your search may yield these items, too. You can skip these because they are not full write-ups of research:

Conference Proceedings
Symposium Publications

Example of a primary research article found in the Library's Academic Search Complete database : (these authors conducted an original research study)

Lumia et al. (2015) Lumia, M., Takkinen, H., Luukkainen, P., Kaila, M., Lehtinen, J. S., Nwaru, B. I., Tuokkola, J., Niemelä, O., Haapala, A., Ilonen, J., Simell, O., Knip, M., Veijola, R., & Virtanen, S. M. (2015). Food consumption and risk of childhood asthma. Pediatric Allergy & Immunology, 26(8), 789–796. https://doi.org/10.1111/pai.12352

Example of a secondary article found in the Library's Academic Search Complete database : (these authors are reviewing the work of other authors)

Rachmah et al. (2022) Rachmah, Q., Martiana, T., Mulyono, Paskarini, I., Dwiyanti, E., Widajati, N., Ernawati, M., Ardyanto, Y. D., Tualeka, A. R., Haqi, D. N., Arini, S. Y., & Alayyannur, P. A. (2022). The effectiveness of nutrition and health intervention in workplace setting: A systematic review. Journal of Public Health Research, 11(1), 1–8. https://doi.org/10.4081/jphr.2021.2312

How do I know if this article is primary?

You've found an article in the library databases but how do you know if it's primary .

Look for these sections: (terminology may vary)

abstract - summarizes paper in one paragraph, states the purpose of the study
methods - explaining how the experiment was conducted (note: if the method section discusses how a search was conducted that is _not_ primary research)
results - detailing what happened and providing raw data sets (often as tables or graphs)
conclusions - connecting the results with theories and other research
references - to previous research or theories that influenced the research

Scan the article you found to see if it includes the sections above. You don't have to read the full article (yet). Look for the clues highlighted in the images below.

Questions? Use Ask a Librarian

Next: Advanced Search-Databases >>
Last Updated: Feb 19, 2024 11:55 AM
URL: https://libguides.polk.edu/primaryresearch

Polk State College is committed to equal access/equal opportunity in its programs, activities, and employment. For additional information, visit polk.edu/compliance .

Identifying Primary and Secondary Research Articles

Primary and Secondary

Primary Research Articles

Primary research articles report on a single study. In the health sciences, primary research articles generally describe the following aspects of the study:

The study's hypothesis or research question
Some articles will include information on how participants were recruited or identified, as well as additional information about participants' sex, age, or race/ethnicity
A "methods" or "methodology" section that describes how the study was performed and what the researchers did
Results and conclusion section

Secondary Research Articles

Review articles are the most common type of secondary research article in the health sciences. A review article is a summary of previously published research on a topic. Authors who are writing a review article will search databases for previously completed research and summarize or synthesize those articles, as opposed to recruiting participants and performing a new research study.

Specific types of review articles include:

Systematic Reviews
Meta-Analysis
Narrative Reviews
Integrative Reviews
Literature Reviews

Review articles often report on the following:

The hypothesis, research question, or review topic
Databases searched-- authors should clearly describe where and how they searched for the research included in their reviews
Systematic Reviews and Meta-Analysis should provide detailed information on the databases searched and the search strategy the authors used.Selection criteria-- the researchers should describe how they decided which articles to include
A critical appraisal or evaluation of the quality of the articles included (most frequently included in systematic reviews and meta-analysis)
Discussion, results, and conclusions

Determining Primary versus Secondary Using the Database Abstract

Information found in PubMed, CINAHL, Scopus, and other databases can help you determine whether the article you're looking at is primary or secondary.

Primary research article abstract

Note that in the "Objectives" field, the authors describe their single, individual study.
In the materials and methods section, they describe the number of patients included in the study and how those patients were divided into groups.
These are all clues that help us determine this abstract is describing is a single, primary research article, as opposed to a literature review.
Primary Article Abstract

Secondary research/review article abstract

Note that the words "systematic review" and "meta-analysis" appear in the title of the article
The objectives field also includes the term "meta-analysis" (a common type of literature review in the health sciences)
The "Data Source" section includes a list of databases searched
The "Study Selection" section describes the selection criteria
These are all clues that help us determine that this abstract is describing a review article, as opposed to a single, primary research article.
Secondary Research Article

Primary vs. Secondary Worksheet

Full Text Challenge

Can you determine if the following articles are primary or secondary?

Last Updated: Feb 17, 2024 5:25 PM
URL: https://library.usfca.edu/primary-secondary

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Biological Sciences: 03-124: Modern Biology Laboratory: Finding Research Articles

Finding Research Articles
Popular Science News Resources
PubMed Tutorial
Google Scholar Tutorial
Citation Management with Zotero

Useful Resource for Accessing Articles

The LibKey Nomad browser extension provides one-click access to the Libraries' full text resources as you find research on the web and in databases. Find information on how to install here .

Types of Scholarly Information

You will encounter many types of articles and it is important to distinguish between these different categories of scholarly literature. Keep in mind the following definitions.

PRIMARY RESEARCH ARTICLE : A primary research article describes an empirical study that aims to gain new knowledge on a topic through direct or indirect observation and research. These include quantitative or qualitative data and analysis. In science, a primary article will often include the following sections: Abstract, Introduction, Methods, Results, and Discussion.

REVIEW ARTICLE : In the scientific literature, this is a type of article that provides a synthesis of existing research on a particular topic. These are useful when you want to get an idea of a body of research that you are not yet familiar with.

PEER-REVIEWED : Refers to articles that have undergone a rigorous review process by peers in their discipline , often including revisions to the original manuscript, before publication in a scholarly journal. Primary research articles in reputable life science journals are always peer-reviewed. Reviews are often peer-reviewed as well.

Useful Journals for this Class

JoVE Biology
Springer Nature Experiments
Current Protocols in Cell Biology
Current Protocols in Molecular Biology

How to Find Research Articles

Research databases.

Research databases are key to conducting comprehensive or specific searches of the scholarly literature across many different publishers and journals. They include special tools and filters to help you narrow and expand your search.

PubMed : PubMed is the most comprehensive source to find scholarly journal articles in biology, health, and medicine. It is maintained by the National Library of Medicine and contains millions of citations and is updated daily with newly published research.
Google Scholar : Google Scholar is a freely available search engine to find scholarly literature in all fields and disciplines. It lacks the many built-in filtering capabilities of subject-specific databases, like PubMed, but can be a useful place to start your research when you are trying to narrow your research topic or to search broadly across many subject areas.

ACADEMIC JOURNALS

You can browse the contents of specific journals in a field by going to the publisher's websites. This is a good way to get to know the type of research being conducted in particular fields. The following academic journals have publicly available articles:

PLOS Biology

To access journals with paid content, you can go directly to the publisher's site and view all the content if you are on campus. If you are off-campus, go to the library homepage and click on Journals & Newspapers. It will give you options for finding articles from different years. You will be prompted to enter you Andrew ID and password but then you can access full-text articles and download PDFs.

Finding Full-Text Articles

Most research articles are not publicly available and require an institutional subscription to access them. If you have citations for specific articles, search for the article in the Library Catalog to see if have access to it. The Catalog will show whether or not we have access to the electronic version and/or the print version. If the CMU library collection doesn't have what you're looking for, you can request an article scan via Interlibrary Loan.

Request materials through Interlibrary Loan by following the instructions for ILLiad.

You can also search for specific articles by putting the article title in the PubMed or Google Scholar databases and following the instructions for finding full-text articles on the PubMed Tutorial and Google Scholar Tutorial tabs of this guide.

If you need help accessing articles, please contact the science librarian team at [email protected].

Search Tips for Finding Relevant Articles

START WITH A REVIEW ARTICLE . Review articles are excellent resources for finding a lot of primary research articles on a given topic. For example, if I'm interested in the development of visual cortical neurons, I could start my search by reading a recent review article on that topic and then look at the references section of the paper to find primary research articles.
FIND ONE OR A FEW RELEVANT PRIMARY RESEARCH ARTICLES . Having even a single relevant article of interest can be very useful in performing a literature search. You can look at the References section of that paper to find older related articles.But how do you find more recent articles that have used and cited the article of interest in their work? You can use Google Scholar to find all of the more recent articles that have cited your article of interest. This is a great way to understand how your article of interest has built on prior research and how it has influenced more recent research. In Google Scholar, you can find related articles by clicking on the " Related Articles " link. In PubMed , you can find related articles by clicking on the title of the article and then the " Similar Articles " link in the right column.

Let's look at the example below. I want to find some relevant articles on the development of visual cortical neurons.

Here, you can see my search for "development of visual cortical neurons" on Google Scholar. In this case, I'm interested in finding a relevant article that is fairly recent so I've set a filter on the left so that only articles published between 2016 and 2018 will appear in my search. The first hit, "Microglial P2Y12 is necessary for synaptic plasticity in visual cortex," looks particularly interesting to me.

I can see that 57 articles have cited this paper and I can click on the Cited by 57 link to see all of those articles. When I click on that link, I see the screen below. I can click on Sort by Date on the left and see that the most recent paper that cited " Microglial P2Y12 is necessary for synaptic plasticity in visual cortex" was published only two days ago! This is an excellent way of finding very recent relevant material. I can also click on the Related Articles link to see articles that are on the same topic. PubMed has a similar link that shows up underneath articles called Similar Articles .

Therefore, by finding a single relevant paper, we can easily find many more relevant articles by looking at the Reference section of " Microglial P2Y12 is necessary for synaptic plasticity in visual cortex" , the Cited by link, and also the Related Articles link. Together, all of these articles will help us understand how the article, " Microglial P2Y12 is necessary for synaptic plasticity in visual cortex," has contributed to the collective body of knowledge on this topic.

<< Previous: Home
Next: Popular Science News Resources >>
Last Updated: Oct 2, 2023 10:41 PM
URL: https://guides.library.cmu.edu/modernbiolab

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Why Search PubMed?

PubMed is the free interface for the premier biomedical database, MEDLINE. It was created & is maintained by the National Library of Medicine. PubMed contains both primary & secondary literature. Because it's a free to access, you can use it even when you leave the University of Michigan.

Articles in PubMed are indexed by MeSH ( Me dical S ubject H eadings), terms that have specific definitions within the database & help you to create more focused searches.

Running a Search

Search Results

Your results are listed on the Search Results page.

You can see that there are many results, including some that are not related to the question.

Search Tip - "Search Details"

What if your search results are not quite what you expected or they seem really off-base? On the Advanced page (link right below the search bar), check Search Details , to see how PubMed "translated" your search.

If at least one term for each concept in your search doesn't map to a MeSH term, you should rethink your search terms or contact the library for help.

The Translations section of Search Details

Look at how some terms were "translated," for example, dietary intake mapped to eating . This is why the search results are so far off topic. We'll need to revise the search.

Revising Your Search

Putting dietary intake and food intake in quotation marks

( "dietary intake" OR "food intake") AND (dairy products OR milk OR cheese OR yogurt)

will restrict this part of the search to those phrases. The phrases won't map to MeSH terms, but may provide a more focused set of results.

And that's exactly what happens.

Search results page from revised search.

Because there are still so many results, add United States to the search:

("dietary intake" OR "food intake") AND (dairy products OR milk OR cheese OR yogurt) AND United States

What's on this page

Choose from this list, or scroll down: Why Search PubMed? ; Running a Search ; Search Results ; Revising Your Search ; Focusing Your Search with Filters ; Search Tip - Keeping Recent Articles in Your Search ; and Search Tip - "Search Details" .

Search Tip - Keeping Recent Articles in Your Search

To be sure that you're seeing the most recent articles on your topic in PubMed, change the default (Best Match) to Most Recent.

Focusing Your Search with Filters

F ilters , which can be found on the left side of the Search Results page, can help you focus your search appropriately. Categories include Article types , Publication dates , Species , Languages , & Ages .

Two filters that are almost always useful are Species / Humans (unless you're looking specifically for animal research) and Language / English . Ages/ Adolescent will also be useful in this search.
Some filters are always readily available: Article type, Text Availability (which you should ignore while you're at Michigan), Publication dates. Others you must add to the filters list.
To add Language , Age , & other types of filters, click on the Additional filters link below the filter list. In the box that opens, select the category of filter & then the specific filters. Click the Show button to make the filters appear on the screen. Next choose the filter(s) you want to add.
When you apply filters, they appear above your search results. You can clear a filter by clicking the name of the filter or the Clear link, or clear all at the top of the results.
Remember to clear all filters when you do a new search.

Message about search filters that have been applied.

Finally, if you want to see more recent articles, add a date filter. Limiting this search to the last 5 years gives 30 results, a reasonable set of results to look through.

Finding Qualitative Research Articles

General Strategies
Grey Literature
Other Resources

Qualitative Research [research that derives data from observation, interviews, or verbal interactions and focuses on the meanings and interpretations of the participants. Year introduced 2003]
Interviews as Topic [conversations with an individual or individuals held in order to obtain information about their background and other personal biographical data, their attitudes and opinions, etc. It includes school admission or job interviews. Year introduced: 2008 (1980)]
Focus Groups [a method of data collection and a qualitative research tool in which a small group of individuals are brought together and allowed to interact in a discussion of their opinions about topics, issues, or questions. Year introduced: 1993]
Grounded Theory [The generation of theories from analysis of empirical data. Year introduced 2015]
Nursing Methodology Research [research carried out by nurses concerning techniques and methods to implement projects and to document information, including methods of interviewing patients, collecting data, and forming inferences. The concept includes exploration of methodological issues such as human subjectivity and human experience. Year introduced: 1991(1989)]
Anecdotes as Topic [brief accounts or narratives of an incident or event. Year introduced: 2008(1963)]
Narration [the act, process, or an instance of narrating, i.e., telling a story. In the context of MEDICINE or ETHICS, narration includes relating the particular and the personal in the life story of an individual. Year introduced: 2003]
Video Recording [the storing or preserving of video signals for television to be played back later via a transmitter or receiver. Recordings may be made on magnetic tape or discs (VIDEODISC RECORDING). Year introduced: 1984]
Tape Recording [recording of information on magnetic or punched paper tape. Year introduced: 1967(1964)]
Personal Narratives as Topic [works about accounts of individual experience in relation to a particular field or of participation in related activities. Year introduced: 2013]
Observational Study as Topic [A clinical study in which participants may receive diagnostic, therapeutic, or other types of interventions, but the investigator does not assign participants to specific interventions (as in an interventional study). Year introduced: 2014]

NOTE: Inconsistent indexing in PubMed. For example, grounded theory articles are not always indexed for qualitative research. Need to TextWord search for additional terms: “grounded theory”, “action research”, ethnograph* etc.

Additional MeSH terms that may be applicable to your topic include: Attitude of Health Personnel ; Attitude to Death ; Attitude to Health ; or Health Knowledge, Attitudes, Practice.

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What improves access to primary healthcare services in rural communities? A systematic review

Zemichael Gizaw 1 ,
Tigist Astale 2 &
Getnet Mitike Kassie 2

BMC Primary Care volume 23 , Article number: 313 ( 2022 ) Cite this article

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To compile key strategies from the international experiences to improve access to primary healthcare (PHC) services in rural communities. Different innovative approaches have been practiced in different parts of the world to improve access to essential healthcare services in rural communities. Systematically collecting and combining best experiences all over the world is important to suggest effective strategies to improve access to healthcare in developing countries. Accordingly, this systematic review of literature was undertaken to identify key approaches from international experiences to enhance access to PHC services in rural communities.

All published and unpublished qualitative and/or mixed method studies conducted to improvement access to PHC services were searched from MEDLINE, Scopus, Web of Science, WHO Global Health Library, and Google Scholar. Articles published other than English language, citations with no abstracts and/or full texts, and duplicate studies were excluded. We included all articles available in different electronic databases regardless of their publication years. We assessed the methodological quality of the included studies using mixed methods appraisal tool (MMAT) version 2018 to minimize the risk of bias. Data were extracted using JBI mixed methods data extraction form. Data were qualitatively analyzed using emergent thematic analysis approach to identify key concepts and coded them into related non-mutually exclusive themes.

Our analysis of 110 full-text articles resulted in ten key strategies to improve access to PHC services. Community health programs or community-directed interventions, school-based healthcare services, student-led healthcare services, outreach services or mobile clinics, family health program, empanelment, community health funding schemes, telemedicine, working with traditional healers, working with non-profit private sectors and non-governmental organizations including faith-based organizations are the key strategies identified from international experiences.

This review identified key strategies from international experiences to improve access to PHC services in rural communities. These strategies can play roles in achieving universal health coverage and reducing disparities in health outcomes among rural communities and enabling them to get healthcare when and where they want.

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Introduction

Universal health coverage (UHC) is used to provide expanding services to eliminate access barriers. Universal health coverage is defined by the world health organization (WHO) as access to key promotional, preventive, curative and rehabilitative health services for all at an affordable rate and ensuring equity in access. The term universal has been described as the State's legal obligation to provide healthcare to all its citizens, with particular attention to ensuring that all poor and excluded groups are included [ 1 , 2 , 3 ].

Strengthening primary healthcare (PHC) is the most comprehensive, reliable and productive approach to improving people's physical and mental wellbeing and social well-being, and that PHC is a pillar of a sustainable health system for UHC and health-related sustainable development goals [ 4 , 5 ]. Despite tremendous progress over the last decades, there are still unaddressed health needs of people in all parts of the world [ 6 , 7 ]. Many people, particularly the poor and people living in rural areas and those who are in vulnerable circumstances, face challenges to remain healthy [ 8 ].

Geographical and financial inaccessibility, inadequate funding, inconsistent medication supply and equipment and personnel shortages have left the reach, availability and effect of PHC services in many countries disappointingly limited [ 9 , 10 ]. A recent Astana Declaration recognized those aspects of PHC need to be changed to adapt adequately to current and emerging threats to the healthcare system. This declaration discussed that implementation of a need-based, comprehensive, cost-effective, accessible, efficient and sustainable healthcare system is needed for disadvantaged and rural populations in more local and convenient settings to provide care when and where they want it [ 8 ].

Different innovative approaches have been practiced in different parts of the world to improve access to essential healthcare services in rural communities. Systematically collecting and combining best experiences all over the world is important to suggest effective strategies to improve access to healthcare in developing countries. Accordingly, this systematic review of literature was undertaken to identify key approaches from international experiences to enhance access to PHC services in rural communities. The findings of this systematic literature review can be used by healthcare professionals, researchers and policy makers to improve healthcare service delivery in rural communities.

Methodology

Research question.

What improves access to PHC services in rural communities? We used the PICO (population, issue/intervention, comparison/contrast, and outcome) construct to develop the search question [ 11 ]. The population is rural communities or remote communities in developing countries who have limited access to healthcare services. Moreover, we extended the population to developed countries to capture experiences of both developing and developed countries. The issue/intervention is implementation of different community-based health interventions to access to essential healthcare services. In this systematic review, we focused on PHC health services, mainly essential or basic healthcare services, community or public health services, and health promotion or health education. Primary healthcare is “a health care system that addressed social, economic, and political causes of poor health promotes health though health services at the primary care level enhances health of the community” [ 12 ]. Comparison/contrast is not appropriate for this review. The outcome is improved access to essential healthcare services.

Outcome measures

The outcome of this review is access to PHC services, such as preventive, promotive, curative, rehabilitative, and palliative health services which are affordable, convenient or acceptable, and available to all who need care.

Criteria for considering studies for this review

All published and unpublished qualitative and/or mixed method studies conducted to improve access to PHC services were included. Government and international or national organizations reports were also included. Different organizations whose primary mission is health or promotion of community health were selected. We included articles based on these eligibility criteria: context or scope of studies (access to PHC services), article type (primary studies), and publication language (English). Articles published other than English language, citations with no abstracts and/or full texts, reviews, and duplicate studies were excluded. We included all articles available in different electronic databases regardless of their publication years. We didn’t use time of publication for screening.

Information sources and search strategy

We searched relevant articles from MEDLINE, Scopus, Web of Science, WHO Global Health Library, and Google Scholar to access all forms of evidence. An initial search of MEDLINE was undertaken followed by analysis of the text words contained in the title and abstract, and of the index terms used to describe articles. We used the aforementioned performance indicators of PHC delivery and the PICO as we described above to choose keywords. A second search using all identified keywords and index terms was undertaken across all included databases. Thirdly, references of all identified articles were searched to get additional studies. The full electronic search strategy for MEDLINE, a major database we used for this review is included as a supplementary file (Additional file 1 : Appendix 1).

Study selection and assessment of methodological quality

Search results from different electronic databases were exported to Endnote reference manager version 7 to remove duplication. Two independent reviewers (ZG and BA) screened out records. An initial screening of titles and abstracts was done based on the PICO criteria and language of publication. Secondary screening of full-text papers was done for studies we included at the initial screening phase. We further investigated and assessed records included in the full-text articles against the inclusion and exclusion criteria. We sat together and discussed the eligibility assessment. The interrater agreement was 90%. We resolved disagreements by consensus for points we had different rating. We used the PRISMA flow diagram to summarize the study selection processes.

Methodological quality of the included studies was assessed using mixed methods appraisal tool (MMAT) version 2018 [ 13 ]. As it is clearly indicated in the user guide of the MMAT tool, it is discouraged to calculate an overall score from the ratings of each criterion. Instead, it is advised to provide a more detailed presentation of the ratings of each criterion to better inform quality of the included studies. The rating of each criterion was, therefore, done as per the detail explanations included in the guideline. Almost all the included full text articles fulfilled the criteria and all the included full text articles were found to be better quality.

Data extraction

We independently extracted data from papers included in the review using JBI mixed methods data extraction form. This form is only used for reviews that follow a convergent integrated approach, i.e. integration of qualitative data and qualitative data [ 14 ]. The data extraction form was piloted on randomly selected papers and modified accordingly. One reviewer extracted the data from the included studies and the second reviewer checked the extracted data. Disagreements were resolved by discussion between the two reviewers. Information was extracted from each included study on: list of authors, year of publication, study area, population of interest, study type, methods, focus of the studies, main findings, authors’ conclusion, and limitations of the study.

Synthesis of findings

The included full-text articles were qualitatively analyzed using emergent thematic analysis approach to identify key concepts and coded them into related non-mutually exclusive themes. Themes are strategies mentioned or discussed in the included records to improve access to PHC services. Themes were identified manually by reading the included records again and again. We then synthesized each theme by comparing the discussion and conclusion of the included articles.

Systematic review registration number

The protocol of this review is registered in PROSPERO (the registration number is: CRD42019132592) to avoid unplanned duplication and to enable comparison of reported review methods with what was planned in the protocol. It is available at https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42019132592 .

Schematic of the systematic review and reporting of the search

We used PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2009 checklist [ 15 ] for reporting of this systematic review.

Study selection

The search strategy identified 1148 titles and abstracts [914 from PubMed (Table 1 ) and 234 from other sources] as of 10 March 2022. We obtained 900 after we removed duplicated articles. Following assessment by title and abstract, 485 records were excluded because these records did not meet the criteria as mentioned in the method section. Additional 256 records were discarded because the records did not discuss the outcome of interest well and some records were systematic reviews. The full text of the remaining 159 records was examined in more detail. It appeared that 49 studies did not meet the inclusion criteria as described in the method section. One hundred ten records met the inclusion criteria and were included in the systematic review or synthesis (Fig. 1 ).

Study selection flow diagram

Of 900 articles resulting from the search term, 110 (12.2%) met the inclusion criteria. The included full-text articles were published between 1993 and 2021. Ninety-two (83.6%) of the included full-text articles were research articles, 5(4.5%) were technical reports, 3 (2.7%) were perspective, 4 (3.6%) was discussion paper, 3(2.7%) were dissertation or thesis, 2 (1.8%) were commentary, and 1 (0.9) was a book. Thirty-six (33%) and 29 (26%) of the included full-text articles were conducted in Africa and North America, respectively (Fig. 2 ).

Regions where the included full-test articles conducted

Key strategies identified

The analysis of 110 full-text articles resulted in 10 themes. The themes are key strategies to improve access to PHC services in rural communities. The key strategies identified are community health programs or community-directed healthcare interventions, school-based healthcare services, student-led healthcare services, outreach services or mobile clinics, family health program, empanelment, community health funding schemes, telemedicine, promoting the role of traditional medicine, working with non-profit private sectors and non-governmental organizations (NGOs) including faith-based organizations (Table 2 ).

Description of strategies

a. Community health programs or community-directed healthcare interventions

Twenty-four (21.8%) of the full-text articles included in this review discussed that community health programs (CHPs) or community-directed healthcare interventions are best strategies to provide basic health and medical care close to the community to increase access and coverage of essential health services. Community health programs are locally based health promotion, disease prevention, and treatment programs available typically to communities in need and community-directed intervention strategy is an approach in which communities themselves direct the planning and implementation of intervention delivery. Rural communities, especially, in developing countries have no access to healthcare facilities in the near distance and have less chance to receive healthcare from doctors, health officers, nurses or midwives. In response to this critical problems, many countries have been investing heavily in community based primary health care to bring services to rural and remote areas where most of the population lives. Community health programs include construction of health posts or community health centers close to the community and deployment of community health workers (CHWs), such as health extension workers, to reach-out every village, who play a prominent role as the gatekeepers of healthcare in rural communities. Community-directed healthcare intervention is an approach in which communities themselves direct the planning and implementation of healthcare interventions. Community participation remains crucial in the identification of health problems, planning or designing of health interventions and implementation of the interventions, which enhances need-based and demand-driven provision of health services while promoting sustainability and ownership (Additional file 2 : Appendix 2, Table A1).

b. School-based primary healthcare

In this review, 9 of 110 (8.2%) of the included full-text articles pointed out that school-based healthcare services can be effective to improve access to PHC services. School-based health services are health programs that offer health care to children and youth either in a school or on school grounds and usually staffed according to school community needs and resources. School-based health services provide a variety of healthcare services to underserved children, youth and vulnerable populations in a convenient and accessible environment. Access to comprehensive health services via schools leads to improved access to healthcare (Additional file 3 : Appendix 3, Table A2).

c. Student-led healthcare services

In this review, 5 of 110 (4.5%) of the full-text articles discussed that the use of medical and health science students as healthcare service providers can minimize problems related with shortage of health professionals in rural healthcare system and can play appreciable roles to minimize healthcare service access problems in rural communities. Student-led healthcare services are developed through consultation between universities and local health providers and are purposefully designed clinical placements with a focus on clinical educational activities for pre-registration students. Student-led clinics link students, healthcare professionals, community-based organizations, universities, and communities. In this approach, students can gain practical experience in an interdisciplinary setting and through exposure to a community with unique and severe needs (Additional file 4 : Appendix 4, Table A3).

d. Outreach services or mobile clinics

In this systematic literature review, 18 of 110 (16.4%) of the included studies discussed that outreach services or mobile clinics in primary care and rural hospital settings can improve access to PHC services in rural communities. Mobile outreach service is defined as healthcare services provided by a mobile team of trained providers, from a higher-level health facility to a lower-level health facilities or locally available community facilities that are not used for clinical services, such as schools, health posts, or other community structures. Outreach services improve access to specialists and hospital-based services, strengthen connections between specialists and PHC providers, and give the benefits of consultations in primary care settings. Specialist outreach services have the potential to overcome access barriers faced by disadvantaged rural and remote communities. Furthermore, a community-based mobile clinics can be effective in uncovering illness and in directing patients to a healthcare home (Additional file 5 : Appendix 5, Table A4).

e. Family health program

Four (3.6%) of the included full-text articles discussed that family health program (FHP) is highly cost-effective tool for improving access to healthcare services for deprived areas (such as rural communities). Family health program means the program is a program designed to provide primary care as well as the prevention and early treatment of communicable and non-communicable diseases in defined populations by deploying interdisciplinary healthcare teams include physicians, nurses, nurse assistants, and full-time community health agents. It has evolved into a robust approach to providing primary care for defined populations by deploying interdisciplinary healthcare teams. The nucleus of each team includes a physician, a nurse, a nurse assistant, and full-time community health agents. This approach is effective on improving access to healthcare and eliminating health disparities (Additional file 6 : Appendix 6, Table A5).

f. Empanelment

This systematic review of literature identified that empanelment (also known as rostering) is a best strategy to proactively provide coordinated primary healthcare towards achieving universal health coverage. Empanelment is a continuous, iterative set of processes that identify and assign populations to facilities, care teams, or primary care providers who have a responsibility to know their assigned population. It enables health systems to improve health outcomes and to reduce costs. Empanelment establishes a point of care for individuals and simultaneously holds primary healthcare providers and care teams accountable for actively managing care for a specific group of individuals (Additional file 7 : Appendix 7, Table A6).

g. Community health funding schemes

In this systematic review of literature, 11 (10%) of the included articles discussed that community health funding schemes such as community-based health insurance (CBHI) increases access to healthcare services in low-income rural communities. Community-based health insurance schemes are usually voluntary and characterized by community members pooling funds to offset the cost of healthcare. Moreover, this approach is effective to mobilize domestic resources for health at low income levels. For low-income countries, community health financing has modest ability to increase the total amount of funds for healthcare. Properly structured community health financing system can significantly improve efficiency, reduce the cost of healthcare, improve quality and health outcomes, and pool risks. Community-financing schemes could improve preventive services and reduce the incidence of diseases. It could also improve people’s access to healthcare and the quality of services, thus improving their health status. Community health financing could also improve risk pooling and reduce health-induced impoverishment. Community health insurance has potential positive impacts on health and social security (Additional file 8 : Appendix 8, Table A7).

h. Telemedicine

In this review, 13 of 110 (11.8%) articles discussed that telemedicine is one of the solutions for rural subspecialty healthcare delivery. Telemedicine can be defined as the use of technology (computers, video, phone, messaging) by a medical professional to diagnose and treat patients in a remote location. The provision of subspecialty services using telemedicine to a remote and medically underserved population provides improved access to subspecialty care. Telemedicine brings sustainable healthcare to rural populations. Use of information and communication technologies in support of health and health-related fields, including healthcare services, health surveillance, health education, and health research has the potential to greatly improve health service efficiency, expand or scale up treatment delivery to thousands of patients in the rural populations (Additional file 9 : Appendix 9, Table A8).

i. Promoting the role of traditional medicine

Seven (6.4%) of the included articles showed that incorporating traditional healers into public health system addresses healthcare needs of people with limited access to allopathic medicine. Traditional medicine is the sum total of the knowledge, skill, and practices based on the theories, beliefs, and experiences indigenous to different cultures, whether explicable or not, used in the maintenance of health as well as in the prevention, diagnosis, improvement or treatment of physical and mental illness. Knowledge about traditional medicine has a catalyzing effect in meeting health sector development objectives. Integrating traditional medicine into national health systems in combination with national policy and regulation for products, practices and providers can enhance access to PHC services in remote populations (Additional file 10 : Appendix 10, Table A9).

j. Working with non-profit private sectors and non-governmental organizations

In this systematic review, 15 of 110 (13.6%) of the included articles revealed that working with non-profit private sectors and NGOs strengthens the healthcare system. Involving the non-profit private sectors, faith-based organizations (FBOs), and NGOs for health system strengthening eventually contributes to create a healthcare system reflecting an increased efficiency, more equity and good governance in health. International and local NGOs have endeavored to fill the gaps in access to healthcare services, research and advocacy. Non-profit private sectors and NGOs have a key role in improving health in low- and middle-income countries. With networks that reach even the most remote communities, many FBOs are well positioned to promote demand and access for healthcare services. Partnership among FBOs is critical in increasing access to healthcare services, and ensuring sustainability by influencing behaviors at the community, family and individual level. Faith-based organizations play an integral role in the healthcare system by increasing health seeking behaviors and delivering supportive services that address common access and cultural barriers (Additional file 11 : Appendix 11, Table A10).

This systematic literature review found that community health programs or community-directed healthcare interventions, school-based healthcare services, student-led healthcare services, outreach services or mobile clinics, family health program, empanelment, community health funding schemes, telehealth, integrative medicine, and working with non-profit private sectors and NGOs are key strategies to improve access to PHC services in rural communities. The identified strategies address the four major pillars of primary healthcare (i.e., community participation, inter-sectoral coordination, appropriate technology, and support mechanism made available) [ 126 ]. Moreover, the identified strategies are effective to improve access to healthcare services to rural communities. Moreover, the identified strategies are effective to solve shortage of manpower and to build knowledge and skill of the local health workforces in rural healthcare system. The ability of a healthcare system to meet health needs of the population depends largely on the knowledge, skills, motivation and deployment of the people responsible for organizing and delivering health services. The results of this review can strengthen the health information system, which are core elements of the healthcare system that ensure community engagement through dissemination and use of timely and reliable health information to rural populations. This review also suggests strategies to narrow down the health disparities among rural populations, which is wide in most Least and Middle Income Countries (LMICs). Healthcare services are usually disproportionately concentrated in major urban areas. As a result, rural communities face growing health disparities, largely attributed to weak policies, inefficiencies, poor leadership, and governance in healthcare system.

This review identified that community health programs or community-directed healthcare interventions address health disparities by ensuring equitable access to health resources in communities where health equity is limited by socioeconomic and geographical factors. Community health programs include identifying and prioritizing public health problems in a specific geographic area; designing and implementing public health interventions (such as establishing community health centers, mobile clinics, and outreach programs); providing services (such as health education, screenings, social support, and counseling), and deploying community health workers to promote healthy behaviors; advocating for improved care for populations at risk; and working with stakeholders to address community healthcare needs [ 16 , 17 , 18 , 127 , 128 , 129 , 130 ]. The community-oriented PHC model which is socially responsive medicine makes a healthcare system more rational, accountable, appropriate, and socially relevant to the public. Consequently, this model serves as a paradigm for reforming healthcare systems. Community-directed interventions can be considered as a realistic means to increase accessibility of interventions at community-level in rural areas [ 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. This approach is best in situations where there are cultural barriers to implement interventions because this strategy is effective to develop ownership in the community. In-service and on-the-job training for community health workers, close supervision and government support, and program evaluation is very important to strengthen the community health program [ 131 , 132 , 133 ].

This review identified that school-based PHC services are effective strategies to improve access to PHC services. School-based health services provide a variety of healthcare services to children, youth and vulnerable populations in a convenient and accessible environment which indirectly improve leadership and governance. Science teachers and home room teachers play important roles to implement this strategy. It impacts on delivering preventive care such as immunizations, managing chronic illnesses and providing reproductive health services for adolescents. Comprehensive health services via schools improve access to healthcare information [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. Access to school around the world increased drastically in the last century [ 134 ]. This high schooling rate is a good opportunity to provide healthcare services to school learners in accessible places and to disseminate health messages to families. Prior researches suggest that school-based healthcare services increase access to healthcare by increasing utilization of primary care, prevention services, and health maintenance visits [ 135 , 136 ]. Including science teachers, home room teachers, school principals, students, communities, community health workers, and other interested parties in the school-based healthcare system as main actors or promoters must be considered to sustain the impact. Health and education sectors should work in collaboration with the above-mentioned actors to plan, implement and monitor the progress. School-based healthcare services are preferable in situations when there is high schooling rate and limited access to healthcare institutions. This strategy is also an alternative way in areas where the health seeking behavior of the community is low.

The use of medical and health science students in rural healthcare system was identified as a key strategy to minimize health inequalities in rural communities due to shortages in health workforce and distribution of healthcare resources [ 49 , 50 , 51 , 52 , 53 ]. Student-led health intervention is an alternative approach to provide essential healthcare services to the community where there is shortage of healthcare workers [ 137 , 138 ]. Students will have opportunities to learn professional skills and competencies while they are providing healthcare services to the community. Moreover, benefits for student learning include increased communication, collaboration, and leadership skills [ 53 , 139 ]. Student-led health intervention also enables increased access to services, more time for assessments and treatments, increased depth of health teaching, holistic and integrated healthcare, and free health supports [ 140 , 141 , 142 , 143 ]. However, the use of medical and health science students in the rural healthcare system may have ethical and competency issues. Supporting strategies such as close supervision, preparing clear protocols, and including senior experts in the team should be considered.

This systematic review of literature found that outreach services or mobile clinics can improve access to PHC service delivery in rural populations [ 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. In developing countries, the highest proportion of people lives in rural areas where doctor services are not available. Rural communities travel to major cities to get specialist services. This reflects a desire for closer integration between primary and secondary care. Specialist outreach services or mobile clinics have become one of the effective solution to solve health disparities, to improve access to healthcare services, and to build capacity of local healthcare workforces. This strategy is preferable in situations when there are high loads in tertiary or referral level hospitals and when there is high patient leakage in the referral system [ 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. However, the implementation may not be easy. It needs well established healthcare system and budget. Moreover, the efficiency of care may be lower compared with hospital-based cares and the effect on patients’ health outcomes might be small [ 56 , 57 , 61 ] . Irregular specialist visits in rural areas may not have real impacts unless the services are sustainable with a strong commitment at national and local levels. Outreach activities should be included in health policies with strong leadership, healthcare financing, and private initiatives must be encouraged to maintain the activities over time.

This review revealed that FHP is highly effective tool for improving health for rural communities. The FHP has provided a new, more robust model of primary healthcare services designed to provide accessible, first contact, comprehensive, and whole person care that is coordinated with other healthcare services. It has positive results to improved availability, access to, and use of health services, and improved health indicators, such as reduced infant mortality, improved detection of cases of neglected diseases, and reduced health disparities [ 73 , 144 , 145 , 146 ]. The FHP deploys interdisciplinary healthcare teams. The team includes a physician, a nurse, a nurse assistant, and full-time community health agents. Family health teams are organized geographically. The teams are responsible for delivering public health interventions [ 72 , 74 ]. Family health program is an alternative strategy in rural healthcare system in situations when there are inequities in access to care; when there is high hospitalization rate; when there is low health seeking behavior in the community; and when there is poor case detecting and reporting system. Despite these remarkable achievements, the FHP has some challenges include difficulties in the recruitment and retention of doctors trained appropriately to deliver primary healthcare, large variations in quality of local care, patchy integration of primary care services with existing secondary and tertiary care, and slow adoption of FHP in large population [ 147 ].

In this review, empanelment has been identified as a best strategy to deliver coordinated primary healthcare towards achieving universal health coverage [ 76 , 77 , 78 , 79 ]. The goal of empanelment is provide people-centered healthcare services based on their needs to ensure that every established patient receives optimal care, whether he/she regularly visits healthcare centers. Major activities in this approach include assignment of all patients to a healthcare provider panel; update panel assignments on a regular basis; and use panel data to educate, and track patients [ 79 ]. Empanelment enables healthcare systems to improve patient experiences, reduce costs, and improve health outcomes. Empanelment is an effective strategy to deliver four key functions: first-contact accessibility, continuity, comprehensiveness, and coordination [ 148 ]. Effective empanelment requires responsibility for the health of a target population, including providing healthcare services based on their health status, which is an important step in moving towards people-centered integrated healthcare [ 79 ].

This review identified that community health funding schemes such as community-based health insurance (CBHI) increases access to healthcare in low-income rural communities. Moreover, this approach is effective to mobilize domestic resources for health at low income levels [ 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 ]. Community-based health insurance is an emerging strategy to provide financial protection against the cost of illness. It is an effective strategy to improve access to quality health services for low-income rural households [ 149 ]. Existence of social capital in the community is a determinant factor for the effectiveness of CBHI as social capital has a positive effect on the community's demand for insurance [ 150 , 151 ]. Moreover, solidarity and trust between the members are the key principles for the good functioning of a CBHI. Solidarity and trust stir-up members who are susceptible to risk to put together their resources for common use [ 149 , 152 , 153 ]. Affordability of premiums or contributions, technical arrangements made by the scheme management, timing of collecting the contributions, trust in the integrity and competence of the managers of the CBHI, The quality of care offered through the CBHI, accessible across different population groups are some of the determinant factors to be considered to increase people’s decision to join the CBHI schemes [ 154 , 155 ].

In this review, telemedicine has been identified as one of the many possible solutions for rural subspecialty healthcare delivery. Telemedicine is a vital technological tool to increase healthcare access, improve care delivery systems, engage in culturally competent outreach, health workforce development, and health information system [ 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 ]. Telemedicine can be a great alternative to the traditional healthcare system in situations like diagnoses of common medical problems; inquiries about various medical issues for home treatments; post-treatment check-ins or follow-up for chronic care; holidays, weekends, late night or any other situation when regular medical care is not possible; patient inability to leave the house; patients who lack regular access to relevant medical expertise in their geographic area ; and etc. However, technological issues are challenges when dealing with telemedicine, especially in developing countries. General problems of Internet connectivity and access to infrastructure can minimize benefits of this strategy. Costs associated with technology can also be a barrier. Furthermore, health technology requires human capacity to use it. Therefore, strengthening the information communication technologies (ICT) and human capacity building on ICT are important to address the health needs of the rural communities.

This systematic review of literature identified that promoting the role of TM solves problems of access to allopathic medicine. Integration of TM in health system will result in increased coverage and access to healthcare services. The role of complementary and alternative medicine for health is undisputed particularly in light of its role in health promotion and well-being. It also supports local health workforces [ 104 , 105 , 106 , 107 , 108 , 109 ]. Incorporating traditional healers into the public health system addresses healthcare needs [ 156 , 157 ]. However, integrating TM to the public healthcare system is challenging. It is a general belief that TM defies scientific procedures in terms of objectivity, measurement, codification and classification [ 157 ]. If integrated, who provides training to medical doctors on the ontology, epistemology and the efficacies of TM in modern medicine [ 157 ]. Due to these, some scholars suggest that both TM and modern medicine be allowed to operate and develop independent of one another [ 158 , 159 ]. Another fundamental challenge to TM is the widespread reported cases of fake healers and healings [ 157 ]. Generally, this strategy is more of feasible in areas where formal trainings on integrative medicine are available. Even though the integration is challenging, the health sector can use traditional healers as health educators or health promoters by providing training and continuous support. It can be also possible to use traditional healers as facilitators in the community-directed approaches. In general TM can be used in the primary healthcare system where no access to allopathic medicine and when conventional medicine is ineffective in treatment of disease [ 160 ].

Working with non-profit private sectors and NGOs has been identified as effective strategies to strengthen the healthcare system in developing countries [ 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 ]. Since governments in developing countries are challenged to meet the health needs of their populations because of financial constraints, limited human resources, and weak health infrastructure; the private sector (especially the non-profit private sectors) and non-governmental organizations can help expand access to healthcare services through its resources, expertise, and infrastructure. However, the presence of an NGO in the operation, may contribute to unrealistic expectations of health services, affecting perceptions of the latter negatively [ 113 ]. Moreover, reports have it that besides other issues in many instances NGOs allocated funds only to disease specific projects (vertical programming) rather than to broad based investments (horizontal programming) [ 161 ]. There are also concerns that donor expenditures in developing countries are not only unsustainable but may be considered as inadequate considering the enormous healthcare burden [ 161 , 162 , 163 , 164 ]. To avoid unrealistic expectations and dissatisfaction, and to increase and sustain the population’s trust in the organization, NGOs should operate in a manner that is as integrated as possible within the existing structure and should work close to the population it serves, with services anchored in the community. Moreover, faith-based organizations contribute in health such as disease prevention, health education or promotion, and community health development beyond psychological and spiritual care [ 119 , 120 , 121 , 122 , 123 , 124 ]. Religious organizations can reach all segments of rural populations. Therefore, integrating PHC services, especially health education and promotion, diseases prevention and community health development with religious organizations intensifies delivery of healthcare services. Working with FBOs is a best way in situations where cultural and faith-based barriers are common and in areas, where access problems are often related to lack of providers. However, religious organizations need intensive training on health promotion and health system to enable them to respond to local contexts within the framework of national policies. Moreover, there should be strong partnership with government agenesis to sustain the effort [ 165 , 166 , 167 , 168 ].

Contribution of this review

Various studies reported one or more strategies to improve access to primary healthcare services. However, the strategies reported by individual studies are not compiled together and there is lack of pooled evidence on effective strategies to improve access to healthcare system. This systematic literature review was, therefore, conducted to compile effective strategies to improve access to healthcare services in rural communities. The review suggests key strategies to improve access to PHC services in rural communities. These suggested strategies are implementable in countries that suffer from shortage of health workers and healthcare financing because all the strategies used locally available opportunities. The local healthcare system needs, therefore, scan the available opportunities in the locality for implementing the suggested strategies and needs to integrate the strategies in the healthcare system to sustain the impacts. Healthcare providers, researchers and policy makers could use the results of this systematic literature review to increase access to healthcare services in hard-to-reach areas. As the strategies are compiled from experiences of different countries (developed and least developed countries), there might be contextual differences like socio-economic, cultural, institutional, and geographical challenges to adopt the identified strategies. Moreover, some of the experiences only come from one or two countries. Therefore, strategy developers and implementers need to consider these contextual challenges or variation during adopting and implementing different strategies.

Strengths and limitations of the study

As a strength, this systematic review explores international (both developed and developing countries) best experiences on primary healthcare service delivery and identified ten key approaches to improve access to PHC services in rural communities. We also searched relevant published or unpublished articles, dissertations or theses, discussion papers, and perspectives from a wide range of sources, such as MEDLINE, Scopus, Web of Science, WHO Global Health Library, and Google Scholar.

As a limitation, we entirely relied on electronic databases to search relevant articles. We didn’t include locally available printed out records. We also applied limits for language. We excluded articles published other than English language. We believed we could get more relevant articles if we had access to records available in prints and if we include articles published other than English language. Furthermore, since the strategies are compiled from experiences of different countries (developed and least developed countries), there might be contextual differences like socio-economic, cultural, institutional and geographical challenges to adopt the identified strategies. There was also limited evidence for some articles, especially reports to rate their methodological quality. Readers should also note that our review might missed some important work in improving access to PHC services and the identified strategies are not the only strategies to improve access to PHC services. There might be other effective strategies which are not included in this review. In addition generalizability might be affected since some of the experiences only come from one or two countries. Moreover, this review focuses on access not quality of care delivered.

This review identified key strategies from international experiences to improve access to PHC services in rural communities. These strategies are effective to improve access to healthcare services in rural or remote communities. They can also play roles in achieving UHC and reducing disparities in health outcomes and increase access to rural communities to get healthcare when and where they want. Therefore, incorporating these key strategies suggested by this review in to the healthcare system is useful to enhance PHC services and to minimize impacts of health disparity in rural communities. However, the identified strategies may not be easy to implement. Increasing number and capacity of human resource for health; strengthening the healthcare financing system; improving medicine and supplies; working in different partners and communities; establishing monitoring and evaluation system; strong and committed leadership; and encouraging private initiatives must be considered to implement and maintain these strategies over time. Moreover, policy makers, program planners and implementers who want to utilize findings of this review should be aware that these are not the only effective strategies to improve access to primary healthcare services.

Availability of data and materials

All the extracted data are included in the manuscript.

Abbreviations

Community-based health insurance

Faith-based organizations

Family health program

Information communication technologies

Mixed methods appraisal tool

Non-governmental organizations

Primary healthcare

Primary Health Care Performance Initiative

Population, phenomena of interest and context)

Traditional medicine

Universal health coverage

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Acknowledgements

The author would like to thank IPHC- E for funding this review.

This review was funded by International Institute for Primary Health Care- Ethiopia (IPHC- E).

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Supplementary Information

Additional file 1: .

Searchstrategy. MEDLINE (PubMed).

Additional file 2: Appendix 2: Table A1.

Description of full-text articles which discussed community health programs or community-directed interventions as a strategy to improve PHC service delivery in ruralcommunities.

Additional file 3:

Appendix 3: Table A2. Description of full-text articles which discussed school-based healthcareservices as a strategy to improve PHCservice delivery in rural communities.

Additional file 4:

Appendix 4: Table A3. Description of full-text articles which discussed student-led healthcareservices as a strategy to improve PHC service delivery in ruralcommunities.

Additional file 5: Appendix 5: Table A4

. Descriptionof full-text articles which discussed outreach services or mobile clinics as astrategy to improve PHC service delivery in ruralcommunities.

Additional file 6:

Appendix 6: Table A5. Description of full-text articles which discussed family health program as astrategy to improve PHC service delivery in rural,communities.

Additional file 7:

Appendix 7: Table A6. Description of full-text articles whichdiscussed empanelment as a strategy to improve PHC service delivery in ruralcommunities.

Additional file 8:

Appendix 9: Table A8. Description of full-text articles which discussed telemedicine or mobile healthas a strategy to improve PHC service delivery in ruralcommunities.

Additional file 9:

Appendix 8: Table A7. Description of full-text articles which discussed community health funding schemes as a strategy to improve PHC service delivery in ruralcommunities.

Additional file 10:

Appendix 10: Table A9. Description of full-text articles which discussed promoting the role of workingwith traditional healers as a strategy toimprove PHC service delivery in rural communities.

Additional file 11:

Appendix 11: Table A10. Description of full-text articles which discussed working with non-profitprivate sectors and non-governmental organizations as a strategy to improve PHC service delivery in rural communities.

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Gizaw, Z., Astale, T. & Kassie, G.M. What improves access to primary healthcare services in rural communities? A systematic review. BMC Prim. Care 23 , 313 (2022). https://doi.org/10.1186/s12875-022-01919-0

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The association of atherogenic index of plasma with cardiovascular outcomes in patients with coronary artery disease: A systematic review and meta-analysis

Mehrdad Rabiee Rad 1 ,
Ghazal Ghasempour Dabaghi 1 , 3 ,
Bahar Darouei 2 &
Reza Amani-Beni 2

Cardiovascular Diabetology volume 23 , Article number: 119 ( 2024 ) Cite this article

259 Accesses

Metrics details

Atherogenic index of plasma (AIP) represents a novel marker in the current era of cardiovascular diseases. In this meta-analysis, we aimed to evaluate the association of AIP with cardiovascular prognosis in patients with coronary artery disease (CAD).

PubMed, Scopus, and Web of Science databases were searched from inception through 2024. The primary outcome was major cardiovascular events (MACE). The secondary outcomes included all-causes death, cardiovascular death, myocardial infarction (MI), stroke, revascularization, and no-reflow phenomenon. AIP was determined by taking the logarithm of the ratio of triglyceride (TG) to high-density lipoprotein cholesterol (HDL-C). The data analysis was represented using the risk ratio (RR) along with a 95% confidence interval (CI).

Sixteen studies with a total number of 20,833 patients met the eligible criteria. The pooled-analysis showed a significant increased risk of MACE in the highest AIP group compared with the lowest AIP group (RR = 1.63; 95% CI, 1.44–1.85; P < 0.001). A similar result was observed when AIP was regarded as a continuous variable (RR = 1.54; 95% CI, 1.30–1.83; P < 0.001). Besides, elevated AIP was associated with increased risk of cardiovascular death (RR = 1.79; 95% CI, 1.09–2.78; P = 0.02), MI (RR = 2.21; 95% CI, 1.55–3.13; P < 0.001), revascularization (RR = 1.62; 95% CI, 1.34–1.97; P < 0.001), no-reflow phenomenon (RR = 3.12 95% CI, 1.09–8.96; P = 0.034), and stent thrombosis (RR = 13.46; 95%CI, 1.39-129.02; P = 0.025). However, AIP was not significantly associated with the risk of all-causes death and stroke among patients with CAD.

Conclusions

The results of this study demonstrated that increased AIP is an independent prognostic factors in patients with CAD. Further research is warranted to elucidate the potential development of targeted interventions to modify AIP levels and improve patient outcomes.

Introduction

Coronary artery diseases (CAD) are accountable for a high morbidity and mortality rate worldwide, with 17.8 million deaths annually [ 1 ]. Many studies have been conducted on the role of risk factors in predicting the risk of CAD; however, fewer studies have addressed the role of various factors in the short and long-term prognosis of patients with CAD. The short-term prognosis is mainly related to percutaneous coronary intervention (PCI) and in-hospital events such as the no-reflow phenomenon and in-hospital death, while the long-term prognosis mainly includes major adverse cardiovascular events (MACE) [ 2 ].

The prognosis of patients with CAD is dependent upon multiple factors. Traditional and modifiable risk factors for CAD include hypertension, diabetes mellitus, smoking, obesity, and dyslipidemia, which have been identified to play a role in the prognosis of CAD and, therefore, MACE [ 3 ]. However, clinicians frequently come across patients with novel CADs that have been misclassified due to these traditional cardiovascular risk factors in a way that necessitates establishing accurate predictors for CAD [ 4 ].

Atherogenic index of plasma (AIP) is calculated by Logarithm [triglyceride (TG) / high-denisity lipoprotein cholesterol (HDL-C)] and can be an independent cardiovascular risk factor by correlating with lipoprotein particle size [ 5 ]. A recent meta-analysis concluded that higher values of AIP can significantly increase the risk of CAD after adjusting for other risk factors [ 6 ]. Moreover, other studies have revealed the prognostic role of AIP in arterial stiffness, atherosclerotic disease, the risk of AMI, ischemic stroke, and MACE [ 7 , 8 , 9 ]. Fu et al. demonstrated that diabetic patients with MACE had higher values of AIP, introducing a novel MACE predictor for high-risk patients [ 10 ]. Similar results were observed in another study, including non-diabetic older adults with hypertension [ 11 ]. Nevertheless, no meta-analysis has been performed to reveal AIP’s prognostic effect in patients with CAD; therefore, we sought to determine the association between the levels of AIP and prognosis in patients with CAD.

Materials and methods

Data sources and searches.

This systematic review and meta-analysis is performed according to the guideline of the Preferred Reporting Items for Systematic Review and Meta-analyses statement (PRISMA) [ 12 ]. A systematic search of the electronic databases including PubMed, Scopus, and Web of Science was undertaken to identify relevant papers published before January 2024. Search strategy used the terms for AIP (“Atherogenic index of plasma”, “atherogenic index”, AIP) and CAD (“coronary disease”, “coronary diseases”, “disease coronary”, “coronary heart disease”, “coronary heart diseases”, “heart disease coronary”, “heart diseases coronary”, “left main”, “left main coronary disease”, “percutaneous coronary intervention”, “coronary artery disease”, “coronary artery diseases”, “coronary artery bypass”, “coronary artery bypass graft”, “coronary syndrome”, “acute coronary syndrome”, “chronic coronary syndrome”). We also conducted a manual search of reference lists and potential related articles. Two independent reviewers completed the electronic search in databases.

Eligible criteria

Two reviewers independently screened the eligible studies based on the following inclusion criteria: (1) Adult patients who were diagnosed with CAD including myocardial infarction (MI), and acute or chronic CAD; (2) Measured AIP and reported the odds ratios (ORs) or hazard ratios (HRs) were with 95% confidence interval (CI) for association of AIP with the outcomes; and (3) The full text was available and written in the English language. Abstracts, reviews, case reports and case series, nonhuman studies, and letters to editors were excluded. Any disagreement was resolved by consensus.

Data extraction and quality assessment

Major adverse cardiovascular events (MACE) was the primary outcome of interest. The secondary outcomes included all-causes mortality, cardiovascular mortality, MI, stroke, revascularization, and no-reflow phenomenon. The following information was abstracted by two independent investigators: the first author’s last name, publication date, sample size, country, study design, mean age, percent of female participants, type of CAD, length of follow-up, adjusted RRs with their 95% CI for the outcomes. Disagreements were resolved by a third reviewer.

Two reviewers independently conducted a quality assessment of each included study using the Newcastle–Ottawa Quality Assessment Scale (NOS), with scores of ≥ 7 considered as high-quality studies [ 13 ]. Any discrepancies were resolved through discussion.

Statistical analyses

Risk ratios (RRs) and 95% CIs from the fully adjusted models were pooled to obtain the association of AIP with the outcomes. In studies where the AIP was examined as categorized variable, the RR of the outcomes for patients with the highest AIP level compared to those with the lowest level were collected. In studies where the AIP was analyzed as a continuous variable, the RR of the outcomes per 1-unit increase in the AIP were extracted.

The I 2 statistic and Cochran’s Q test were utilized to assess heterogeneity. In cases where significant heterogeneity was observed (I 2 > 50%, p < 0.1) among the studies, a random-effects model was applied. A fixed-effects model was used in case of no significant heterogeneity. Visual inspection of Funnel plot and Egger test were used to evaluate possible publication bias. We performed subgroup analysis to identify the potential sources of heterogeneities. All data were analyzed with STATA (Version14). P value < 0.05 was considered as significant.

Following the abovementioned systematic search, we identified 1067 papers through databases. After duplicates removing and title/abstract screening, 118 studies eligible for full-text evaluation. After full-text screening, 16 studies [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] were included (Fig. 1 ).

The flowchart of study selection

Characteristics of included studies

The basic characteristics of included studies are summarized in Table 1 . Sixteen studies with a total of 20,883 participants were published from 2020 to 2024. Twelve studies were retrospective cohort, three studies were prospective cohort, and one study was cross-sectional. The mean age and female proportion ranged from 55 to 63 years and 14.7–41.1%, respectively. The duration of follow-up ranged from three day to four years. All included studies evaluated the AIP under fasting condition. According to NOS score, all included studies had high quality (score ≥ 7).

Primary outcome

A total of eight studies investigated the association of AIP as a continues variable and MACE in patients with CAD. Overall, AIP level was found to increase the risk of MACE (RR = 1.54; 95% CI, 1.30–1.83; P < 0.001) with a significant heterogeneity (I 2 = 61.9%, P = 0.010) (Fig. 2 ). Six studies compared the highest vs. lowest category of AIP, and the pooled analysis showed an increased risk of MACE in those with higher AIP (RR = 1.63; 95% CI, 1.44–1.85; P < 0.001) with no significant heterogeneity (I 2 = 40.0%, P = 0.134) (Fig. 2 ).

Forest plots showing the meta-analysis of major cardiovascular events using the AIP as categorial and continues variable

Secondary outcomes

Ten studies reported the RRs for the secondary outcomes. The pooled analysis indicated that higher AIP increase the risk of cardiovascular death (RR = 1.79; 95% CI, 1.09–2.78; P = 0.02), MI (RR = 2.21; 95% CI, 1.55–3.13; P < 0.001), revascularization (RR = 1.62; 95% CI, 1.34–1.97; P < 0.001), and no-reflow phenomenon (RR = 3.12 95% CI, 1.09–8.96; P = 0.034). However, AIP was not significantly associated with risk of all-causes death (RR = 1.15; 95% CI, 0.56–2.36; P = 0.699) and stroke (RR = 1.03; 95% CI, 0.69–1.52; P = 0.892) (Fig. 3 ). A significant heterogeneity was found for the no-reflow phenomenon (I 2 = 89.7%, P < 0.001). Three studies analyzed AIP as a continuous variable, which reported an of HR 1.21 (95% CI, 0.72–2.02, P = 0.460), 1.61 (95% CI, 1.12–2.32, P = 0.009), 3.77 (95% CI, 1.34–10.60, P = 0.012), and 13.46 (95%CI, 1.39-129.02; P = 0.025) for cardiovascular death [ 17 ], MI [ 17 ], all-causes death [ 21 ], and stent thrombosis [ 24 ], respectively.

Forest plots showing the meta-analysis of secondary outcomes in comparison of highest AIP vs. lowest AIP group

Subgroup and sensitivity analysis

A subgroup analysis was performed for primary outcome according to the age (< 60 or ≥ 60 years), study design (retrospective or prospective), sample size (< 1,000 or ≥ 1,000), duration of follow-up (< 24 or ≥ 24 months), and LDL-C (< 1.8 or ≥ 1.8 mmol/L) to identify the sources of heterogeneity. A remarkable reduction in heterogeneity was found in prospective studies (I 2 = 0.0%) and LCL-C below 1.8 mmol/L (I 2 = 0.0%), suggesting that study design and LDL-C level might be factors contributing to heterogeneity. Besides, the analysis revealed no significant association between AIP and MACE in studies with a duration of follow-up below 24 months (RR = 1.56; 95% CI, 0.85, 2.87; P = 0.150) and mean age of over 60 years (RR = 1.43; 95% CI, 0.72, 2.82; P = 0.305) (Table 2 ).

A sensitivity analyses was performed including studies with a ≥ 2 years of follow-up. Consistent with our primary analysis, we revealed a significant association of AIP with MACE (RR = 1.66; 95% CI, 1.25, 2.20, P = 0.001). The results for other outcomes remained unchanged except for no-reflow phenomenon, which all studies reported a short duration of follow-up, and hence, the further analysis could not perform.

Publication bias

The funnel plots in Fig. 4 demonstrate the relationship between the AIP and the incidence of MACEs in CAD patients. Upon visual examination, the plots seem to be asymmetrical, suggesting a possible risk of publication bias. However, Egger test found no significant publication bias for categorial ( P = 0.052) and continues ( P = 0.178) analysis.

The publication bias assessment with funnel plot for the primary outcome

This meta-analysis showed that a higher AIP is associated with an increased risk of MACE, cardiovascular mortality, MI, revascularization, and the no-reflow phenomenon in patients with CAD. Subgroup analysis revealed that AIP may not be an indicator of MACE among patients aged ≥ 60 years and short follow-up times. Besides, AIP was not associated with all-causes mortality and stroke risk.

In this study, CAD patients with a higher AIP level had a < 1.5-fold higher risk for MACE compared with subjects with lower AIP. In line with our results, a fifteen-year cohort study conducted on 6323 healthy adults demonstrated a 1.2-fold greater risk for cardiovascular events among participants with higher AIP [ 30 ]. Moreover, a cross-sectional study compromising 7,362 adults showed that the third tertile of AIP had a 1.3-fold higher risk for cardiovascular disease compared to the first tertile [ 31 ]. These collective findings underscore the potential of AIP as a valuable biomarker for identifying individuals at higher risk for cardiovascular disease.

Our subgroup analysis did not detect a significant association between AIP and MACE in older patients. In this context, Nansseu et al. [ 32 ] enrolled 108 postmenopausal women, and found no significant correlation between AIP and cardiovascular risk evaluated with Framingham risk score. Similarly, there was no significant association between AIP and CAD in elderly females aged ≥ 65 years [ 33 ]. Moreover, AIP could not predict the presence of CAD in elderly males who underwent coronary angiography [ 34 ]. A possible explanation to address this finding is that AIP level is increased in elderly population [ 35 ]. Several studies showed a positive correlation between AIP and age among different populations [ 36 , 37 , 38 ], which might impact the likelihood of detecting a significant association between AIP level and cardiovascular events in this group. Further studies are warranted to better understand the impact of age on AIP levels and its implications for assessing cardiovascular risk in the elderly.

This meta-analysis included three studies evaluating the association of AIP as a categorial variable with all-causes death, and the results showed that AIP could not predict all-causes death in patients with CAD. However, Refs. [ 16 , 26 , 29 ]) considered AIP as a continuous variable, and found a significant positive correlation between AIP level and risk of all-causes mortality [ 21 ]. This discrepancy may be due to low number of studies and the differences in follow-up duration between the studies. The endpoint of et al. was the in-hospital mortality, and hence, their results showed the predictive value of AIP for all-causes mortality in a median follow-up duration three days. To evaluate the association of AIP with risk of short-term mortality, further studies are needed.

The disbalance of these plasma lipids leads to dyslipidemia, which is characterized by high levels of LDL-C, TG, and total cholesterol and low levels of HDL-C [ 39 ]. Although reducing LDL-C levels is a treatment goal in CAD, even after attaining this target, a notable residual cardiovascular risk remains present, encouraging the exploration of more accurate risk factors in these patients [ 40 ]. Regarding a practical predictor, the AIP strongly predicts cardiovascular events by reflecting the atherogenic lipid profile and providing valuable insights into the residual cardiovascular risk.

Despite the strengths of this study, including a comprehensive search strategy and evaluating several outcomes, there are limitations that should be considered. First, the majority of studies included in this meta-analysis were retrospective, and hence, further studies with prospective design are needed. Second, the presence of significant heterogeneity in some of the analyses suggests potential variations in methodologies and outcome definitions such as MACE, which may have influenced the results. Third, although this study found a significant association of AIP with MI and cardiovascular death, there was considerable variability across studies. As such, additional validation is required to confirm this tenuous relationship. Finally, the included studies were observational, which limits the ability to establish causal relationships between AIP and cardiovascular outcomes.

In conclusion, the findings of this meta-analysis support the notion that AIP is a potential prognostic marker for adverse cardiovascular events in patients with CAD. A higher AIP was consistently associated with an increased risk of MACE, cardiovascular death, MI, revascularization, and the no-reflow phenomenon. Notably, no association was found between AIP and all-causes death or stroke. These results have important implications for risk stratification and management strategies in CAD patients. Further research is needed to validate these findings.

Data availability

No datasets were generated or analysed during the current study.

Abbreviations

Atherogenic index of plasma
Coronary artery disease

High-density lipoprotein cholesterol

Hazard ratio

Low-density lipoprotein cholesterol

Percutaneous coronary intervention

Preferred Reporting Items for Systematic Review and Meta-analyses statement

Small dense low-density lipoprotein

Triglyceride

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Interventional Cardiology Research Center, Cardiovascular Research Institute, Isfahan University of Medical Sciences, Isfahan, Iran

Mehrdad Rabiee Rad & Ghazal Ghasempour Dabaghi

School of Medicine, Isfahan University of Medical Science, Isfahan, Iran

Bahar Darouei & Reza Amani-Beni

Isfahan Cardiovascular Research Center, Cardiovascular Research Institute, Isfahan University of Medical Sciences, Isfahan, Iran

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MRR and GGD designed the research. MRR, RAB, and BD collected data in electronic database. MRR performed statistical analysis. All authors contributed to drafting of the manuscript, had full access to all the data in the study, approved the final version of the manuscript and had final decision to submit for publication. All authors read and approved the final manuscript.

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Rabiee Rad, M., Ghasempour Dabaghi, G., Darouei, B. et al. The association of atherogenic index of plasma with cardiovascular outcomes in patients with coronary artery disease: A systematic review and meta-analysis. Cardiovasc Diabetol 23 , 119 (2024). https://doi.org/10.1186/s12933-024-02198-y

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