Since 1975, NLM has included author-written abstracts from journals whose publishers gave the NLM permission for their use. These abstracts appear in the Abstract (AB) field. Over 50% of the documents in Ovid MEDLINE® contain abstracts.

The abstract index contains all searchable words from the abstract.

The Authors (AU) field contains the authors of the article. The format for authors is last name followed by one or more initials: Smith JC or Smith J. Enter the last name, or if it is a common name, enter the last name and first initial. If you are unsure of the spelling of the last name (macdonald or mcdonald), enter one version and then scroll through the list of names to find the other.

Misspelled and corrected names are also included in the Authors Index to ensure all possible matches. Only correct author names display, while incorrectly spelled names are indexed along with the correct spelling of the name.

The Comments (CM) field contains an indication that the article either contains a comment on another article or is commented on in another article. The CM field begins with the indication "Comment On" or "Comment In" and then displays the Journal Abbreviation (JA), Date of Publication (DP), the Volume (VO), Issue/Part (IP), and Page (PG).

Articles that contain a comment display with [comment] appended to the end of the article title. Articles that are commented on in another article display with [see comment] appended to the end of the article title.

The Digital Object Identifier (DO) field contains a unique and persistent digital identification code for any object of intellectual property.

The DOI itself consists of two parts: a prefix which is assigned to each publisher by the administrative DOI agency, such as 10.1097, and a suffix which is assigned by the publisher and can be any code that the publisher chooses, such as 00045415-200111000-00002. The full DOI appears as such: 10.1097/00045415-200111000-00002.

Search all DOI's by replacing punctuation with spaces such as "10 1016 j adnc 2003 08 001".do. for the displayed DOI of 10.1016/j.adnc.2003.08.001.

The DOI field will be used only for new records added during the 2008 production year.

Note: NLM has not announced when DOIs will begin to appear in records.

The ISSN Electronic (ES) field contains the Electronic International Standard Serial Number (EISSN) for the journal in which an article was published. It appears as an 8 digit number, separated by a hyphen, such as 0028-4793. To retrieve all of the articles for a journal, search by the Journal Name (JN).

Both Electronic and Print ISSNs can be searched in the ISSN Print (IS) field.

The Authors Full Name (FA) field contains the full name of the authors of the article when available.

Subheadings are qualifiers added to MeSH subject headings to refine their meaning.  Terms such as "etiology" or "therapy," when combined with a MeSH heading, give a precise idea of what an article covers.

The Floating Subheadings (FS) field contains both the 2-letter codes, such as po, and the full heading, such as poisoning. These are displayed following the corresponding MeSH Subject Headings.

The Gene Symbol (GS) field contains gene symbols as they are entered into MEDLINE in the original document. They often, but not always, conform to standardized human gene nomenclature. Ignore super or sub-scripts in entry of a gene symbol: psub 1450 would be entered p1450. Enter hyphens as in the original symbol.

The Gene Symbol field was added to MEDLINE in 1991. Beginning in 1996, data is no longer added to this field.

The Subject Heading Word (HW) index allows you to retrieve every MeSH Subject Heading (SH) and Publication Type (PT) that include a particular word. Do this by searching a single word in the Subject Heading Word field.

The Investigator Affiliation (IA) field contains the affiliation of the investigator of the article, and displays as part of the Institution (IN) field.

The ISSN Linking (IL) field is used to link multiple versions of a record, such as the print and online versions of a journal. The ISSN used for linking is the first ISSN assigned to a resource.

The ISSN Linking field will be used only for new records added during the 2008 production year.

Note: NLM has not announced when Linking ISSNS will begin to appear in records.

The Institution (IN) field contains the primary author's affiliation, which is usually the source for a reprint of the article. This index also contains the investigators affiliation. This information can be searched in most documents since 1988, but records from earlier years which were added to the database after 1988 may also contain institution information. Beginning with documents indexed in 1996, the primary author's email address will also be included, if present in the journal.

The information is taken from the source document and is not standardized. Enter the single most descriptive word in an institution (harvard, rather than university). Consider both full spellings and abbreviations.

The Investigator (IR) field contains personal names of individuals (such as collaborators and investigators) who are not authors of a paper but rather are listed in the paper as members of a collective/corporate group that is an author of the paper. The format for authors is last name followed by one or more initials:  Smith JC or Smith J.

The ISSN Print (IS) field contains the International Standard Serial Number (ISSN) for the journal in which an article was published. It appears as an 8 digit number, separated by a hyphen, such as 0028-4793. To retrieve all of the articles for a journal, search by the Journal Name (JN).

Both Electronic and Print ISSNs can be searched in the ISSN Print field.

The Journal Abbreviation (JA) is the journal title abbreviation that is displayed in the Abbreviated Source (AS) field and cannot be searched.

The Journal Name (JN) field contains the full name of the journal in which the article was published. Journal names are indexed as phrases, so enter enough letters of the journal name to locate the name in the index, as in new engl (for New England Journal of Medicine).This field displays as part of the Source (SO) field.

If the first word of a Journal Name is “The”, it has been removed.

The Locally Held (LH) field indicates (with a Y or an N) if a journal is held in your local library system.

The Local Messages (LM) field contains messages created by the System Administrator to indicate information about journals held in your local library system.

The Name of Substance (NM) field contains single words from the CAS Registry Number/EC Number (RN) field and is used to search portions of chemical names. This field displays as part of the CAS Registry Number/EC Number (RN) field.

The Name of Substance field was added to MEDLINE in 1980.

The General Note (NT) field contains general supplementary information about an item. The notes may include information on the availability of a bibliography, ordering information for dissertations or hearings, or general summaries of materials such as manuals or scripts. A series title may appear for a book or for audiovisual materials.

The Other Abstract (OA) field includes a brief abstract written by collaborating partners. The OA field is indexed in Abstract (AB) field, and contains all searchable words from the other abstract. Collaborating partners include:

The Primary Author (PA) field contains the first author listed for the article.  This allows users to search for articles by any primary author. Author names display in Authors (AU) and Authors Full Name (FA) fields.

Searching for smith rh.pa. will return results where "Smith RH" was listed as the main author of the article.

The Publisher (PB) field contains publisher information for books, monographs or any non-journal publications. This information is taken from the source document as it appears, so variant forms of a publisher are possible.

This field is usually displayed as part of the Source (S0) field.

The Page (PG) field consists of the inclusive pagination of a journal article. Often a journal title combined with the beginning page number is enough to locate a citation. You can search for pages with alphanumeric characters, such as "a1.pg."

This field displays as part of the Source (SO) field.

The Personal Name As Subject (PN) field displays the name of a well-known person if they are discussed in an article, such as an interview or obituary.

The format for Personal Name is the same as for Author (AU) -- last name and initials: Bach JS. Enter a last name and one initial if known.

In addition to indexing documents with Medical Subject Headings, the indexers at the National Library of Medicine assign terms to describe the article type. Publication Types include such classifications as reviews, clinical trials, directories and letters. These terms appear in the Publication Type (PT) field.

To view the index, enter enough letters to distinguish a publication type (jour for "journal article"); the entire index is quickly scrollable to determine all possible publication types.

With the 2005 reload, Publication Types are also loaded into the MeSH. Because some Publication Types are also MeSH terms, the syntax to enter the Tree is "Randomized controlled trial [publication type]". To post the results from the Tree without entering the Tree, the syntax is: "Randomized controlled trial [publication type]"/ or Randomized controlled trial.pt.

The CAS Registry/EC Number/Name of Substance (RN) field contains the Chemical Abstracts Service Registry number or Enzyme Commission number for a compound mentioned in an article. If the generic compound name can be determined, it is included. The RN field was added to Ovid MEDLINE in 1980. 

Registry numbers appear with hyphens, such as 50-00-0. Search for EC numbers in the format ec 1 1 1 1 adh1c protein human. Chemical names appear with all special characters except hyphens removed.

The Record Owner (RO) field contains the owner of the record.

The Secondary Source AN (SA) field contains the unique accession number for external resources mentioned in a MEDLINE record. The display includes the Secondary Source ID (SI) and the accession number seperated by a forward slash (/).

If you wish to search all works from a particular databank use the Secondary Source ID (SI) field.

The Journal Subset (SB) field identifies the subset for MEDLINE records from certain journal lists or records on specialized topics. Some of these values are found on extremely small numbers of records. Citations may contain more than one occurrence of this field. The value is true at the time the record was created. If the status of a journal changes, the value on the record does not change.

Subset field values and their definitions are as follows. Note that several are closed subsets no longer being assigned.

The MeSH Subject Headings (SH) field contains the Medical Subject Headings used by indexers at NLM to describe the content of an article. NLM's MeSH terms are organized in a hierarchy, or "tree" structure.

MeSH headings are entered into the index as phrases and should be searched as they appear in the NLM MeSH books or in the Tree tool display.

The Secondary Source ID (SI) identifies secondary source databanks with unique identifiers of external resources mentioned in a MEDLINE record. The field is composed of the source acronym, such as GENBANK.

The Secondary Source Linking (SL) field contains the URL to ClinicalTrials.gov and ISRCTN resources mentioned in MEDLINE records.

The Source (SO) field includes a display of all the basic information needed to locate a record, including:

The Status (ST) field contains the status of the citation.

The Text Word (TW) field is an alias for all of the fields in a database which contain text words and which are appropriate for a subject search.

The Text Word field in MEDLINE includes Title (TI) and Abstract (AB).

The Unique Identifier (UI) field contains an 8-digit number assigned by NLM to uniquely identify a particular record. This number is also the one used to locate the document through NLM's document delivery service. This number was formerly the PubMed Identifier (PMID).

PubMed no longer supplies PMID numbers with the input data. You can search for PMID and UI pairs using NLM's Matcher tool, located on NLM's website at http://eutils.ncbi.nlm.nih.gov/entrez/publisher/uidpmid.cgi/.

You can also download a full table of PMID numbers and their related Unique Identifiers can be found at ftp://ftp.ncbi.nlm.nih.gov/pubmed/. This location includes 6 .zip files that comprise the full table of pairs:

The Exploded Subheadings (XS) field displays the two-letter codes for the pre-exploded subheadings.

Sometimes multiple MeSH Subheadings can be logically grouped together. Such related groups of subheadings are "pre-exploded" under one broad subheading. This means that all the grouped subheadings can be retrieved together by searching on the "pre-exploded" version of the broad subheading. These pre-exploded MeSH Headings are displayed in the MeSH Subject Headings (SH) field.