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2006 MAY–JUNE; 350
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May 12, 2006 [posted]
July 24, 2006 [Editor's note added]
July 24, 2006 [Editor's note added]

NIH Grant Numbers in PubMed® Citations

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ational Institutes of Health (NIH) grant numbers can be searched in PubMed as follows (where "hl" in the examples is the letters h and l):

Search PubMed For Format Example
Individual NIH grant number 8-character string hl060133[gr]
Broader search 2-letter code assigned to the institute/agency hl[gr]
Broadest search institute/agency abbreviation nhlbi[gr]

Journal articles often indicate support of the reported research by a funding agency. When the funding support is from the Public Health Service (PHS) agencies of the United States Federal Government, the National Library of Medicine (NLM) has routinely included the grant or contract number(s), as published in the journal article, in the MEDLINE/PubMed citation since 1981.

The National Institutes of Health (NIH) is part of the PHS; PHS also includes the Centers for Disease Prevention and Control (CDC) and the Food and Drug Administration (FDA) among other agencies.

PHS grant/contract numbers in PubMed consist of three components:

  1. the grant/contract number,
  2. a 2-letter code for the funding agency, and
  3. the abbreviation for the funding agency.


The PubMed Citation and MEDLINE displays show these numbers. Here's an example:

        R01 HL60133/HL/NHLBI

Authors and publishers present the grant numbers in a variety of formats. NLM does not attempt to standardize the format of the published grant numbers. The data are only as accurate as the original source. [Editor's Note: In July 2006, NLM edited the prefix of NIH grants numbers in citation data to change the letter 'O' to the number '0' (zero) because the number is the correct format, e.g.: RO1 was changed to R01. At the same time, NLM instituted data entry validations to enforce the number in newly created citations. This means that the grant number data in the online citations may no longer match what is in the published article, which was generally published incorrectly.] However, additional search access points are generated to facilitate searching in PubMed.

The traditional format for an NIH grant number typically has three main pieces:

  1. a prefix, followed by
  2. a 7- or 8-character string (now consisting of a 2-letter code for the administering organization and a 5- or 6-digit number), followed by
  3. a suffix (usually a hyphen and another numerical or alphanumerical string which may include the year of funding).

Here are some of the ways that the grant number R01 HL060133-01 appears in MEDLINE/PubMed citations:

R01 HL60133 PMID: 15611013 Note 7-character string, not 8.
R01 HL-60133 PMID: 15345532 Note inserted hyphen.
RO1 HL-60133 PMID: 15465866 Note incorrect letter O, not zero, in R01 prefix.
R01 HL60133-01 PMID: 15345581 Note funding year suffix portion.
R01 HL 60133 PMID: 11956246 Note inserted blank space.
RO1-HL-60133-01 PMID: 11701509 Note letter O, not zero, in prefix and inserted hyphens.
RO1 HL60133-01 PMID: 11090548 Note letter O, not zero, in prefix.
HL60133 PMID: 10096885 Note missing prefix.

[Editor's Note: The examples in the above table that illustrate the letter "O" in the R01 prefix were all corrected in July 2006. The links now show the corrected data using a zero in place of the letter, which is the correct format.]

The best way to search PubMed for an individual NIH grant number is to use an 8-character string portion with the search tag [gr]. The trick is to remember to use an 8-character string starting with the 2-letter code for the institute and the 6-digit portion with no spaces or hyphens. That 6-digit portion is often published as only a 5-digit portion minus the leading zero which you will have to insert for the most comprehensive retrieval. Using the example above, the recommended search is:

         hl060133 [gr]

As of May 8, 2006, this search retrieved 22 citations. The eight variations listed above each retrieved from one to six citations, all of which are retrieved by the recommended search string.

You may also search grant numbers in groups represented by either the 2-letter code for the institute (e.g., HL is a code for the National Heart, Lung, and Blood Institute) or the agency/institute abbreviation. While many institutes have only one 2-letter code, some have more than one, which means that the agency/institute abbreviation search would be the larger retrieval.

For example, the National Heart, Lung, and Blood Institute (NHLBI) currently has seven 2-letter grant codes:

         hl [gr] retrieves nearly 183,000 citations
         nhlbi [gr] retrieves over 187,000 citations

All citations from the former search are part of the latter search. The latter search also retrieves citations indicating NHLBI support using one of its other codes (e.g., HV, HB). The list of 2-letter grant codes is found through the Appendices of the PubMed Help or at this URL: http://www.nlm.nih.gov/bsd/grant_acronym.html

The NIH Public Access plan enables NLM to associate NIH grant numbers with author manuscripts submitted to PubMed Central®. The grant numbers derived from this process are also included in PubMed citations to the final, published article. NLM began to add these grant numbers on March 24, 2006. This may result in multiple versions of the same intellectual number on one citation (some from the published article and some from the NIH Public Access submission). For example, the spacing, punctuation, or ending numbers that indicate the funding year may vary.

It's important to note that indexers add MeSH headings based on the information found in the published article. For this reason, the corresponding Research Support, N.I.H., Extramural or Research Support, N.I.H., Intramural headings (or Research Support, U.S. Gov't, P.H.S. heading prior to June 2005 data entry) will not be added to the citations if the grant number is derived only from the NIH Public Access submission process. NLM also does not routinely add a heading before its introduction date. A comprehensive search for NIH-supported research must, therefore, include the 2-letter codes and agency abbreviations as well as the MeSH headings.

The Web page Funding Support - 2006 may be of interest. It explains the relationship between grant numbers and the MeSH (Medical Subject Headings) research support terms, and provides the strategy for the 2-letter codes and agency abbreviations ORed with the two NIH-specific MeSH headings.

The articles Wellcome Trust Grant Number Added to MEDLINE®/PubMed® Data. NLM Tech Bull.2006 May-Jun;(350):e4. and MeSH® Category V Terms: Change in Treatment from MeSH Heading to Publication Type During Year-End-Processing for Both MEDLINE® and NLM Catalog. NLM Tech Bull. 2006 Sep-Oct;(352):e2.may also be of interest.

By Lou Wave S. Knecht
Bibliographic Services Division

Knecht LS. NIH Grant Numbers in PubMed®. NLM Tech Bull. 2006 May-Jun;(350):e3.