Skip to main content
U.S. flag

An official website of the United States government

Here’s how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

This is a preview of updates coming to the Technical Bulletin's website in early December 2025. Return to current site.
Read more about the modernization release schedule in this announcement.
Comment via the yellow feedback button in the lower right hand corner of the page. Contact the NLM Help Desk with any questions or concerns.

This is archived content.

Links may have become inactive over time. Visit Archive-It   to find the original published layout.

Definition of Structured Abstracts Expanded to Enhance Readability

Knecht LS, Ripple AM, Tybaert S. Definition of Structured Abstracts Expanded to Enhance Readability. NLM Tech Bull. 2013 May-Jun;(392):e6.

June 25, 2013 [posted]
July 18, 2013 [Editor's note added]

In 2010, structured abstracts in PubMed were reformatted for easier readability with bolded, uppercase section labels followed by a colon beginning on a new line. NLM previously defined a Structured Abstract to be:

". . . one that contained at least 3 labels that represented 3 distinct concepts (e.g., "INTRODUCTION," "METHODS," "CONCLUSIONS"), of which 1 must be considered an ending concept (such as "RESULTS" or "CONCLUSIONS").

To enhance readability, NLM's new definition of Structured Abstracts is:

...one that has at least one label that:

To accommodate this broadened definition, NLM made a mid-year 2013 change to the NLMMedlineCitationSet DTD (used for MEDLINE/PubMed processing) which added a new NlmCategory attribute valid value, UNASSIGNED. The UNASSIGNED NlmCategory is used for labels in structured abstracts that NLM has not yet mapped to one of five categories, i.e., BACKGROUND, OBJECTIVE, METHODS, RESULTS, CONCLUSIONS.

Prior to expanding the definition of structured abstracts to include abstracts that contain fewer than three labels and adding the UNASSIGNED valid value, the display of these abstracts remained in a single paragraph format (see Figure 1).

Screen capture of citationcontext menu.
Figure 1: Abstract in single paragraph format but with two labels.

After expanding the definition of structured abstracts to include abstracts that contain fewer than three labels and UNASSIGNED mapping, these abstracts are also reformatted for easier readability. Section labels remain in uppercase followed by a colon, and are bolded with each section beginning on a new line (see Figure 2).

Screen capture of citationcontext menu.
Figure 2: Reformatted PubMed Structured Abstract having fewer than three labels.

These PubMed structured abstracts having fewer than three labels will be added to the PubMed search feature that allows for a search of structured abstracts. [Editor’s Note: The following sentence was changed on July 18, 2013.] Effective June 21, 2013, citations with the status of publisher, i.e., publisher[sb], that have structured abstracts are also included in these search results.

Researchers or licensees who wish to continue using the stricter definition of structured abstracts may do so. The Structured Abstracts in MEDLINE Web site continues to have the Updated Label List and NLM Category Mappings, which contains the vetted structured abstract labels and their mapped-to NlmCategories, i.e., BACKGROUND, OBJECTIVE, METHODS, RESULTS, CONCLUSIONS. NLM will continue to create the NLM category mapping file. New labels with the "UNASSIGNED" NlmCategory may eventually be mapped and added to future versions of the NLM Category Mappings file.