The Index to the NLM Classification is a single index to the schedules, which consists primarily of Medical Subject Headings (MeSH) terms used in cataloging. MeSH is the National Library of Medicine’s controlled vocabulary thesaurus that gives uniformity and consistency to the indexing and cataloging of biomedical literature.

All main index headings are MeSH. However, not all terms available in MeSH are reflected in the Index. Index terms are included based on literary warrant reflected in the NLM collection. MeSH Supplementary Concept Records (SCRs) are not used in cataloging and are therefore excluded from the index. Non-MeSH terms are used as cross references to provide additional access for alternative ways to express a concept.

The MeSH entries in the Index are updated annually to be consistent with the latest edition of MeSH. The Index links out to MeSH terms in the MeSH Browser and to classification numbers in the Schedule.

The index terms are arranged in alphabetical order with Roman numerals filed as letters in this arrangement. Arabic numerals are found at the beginning of the Index. The index entries include NLM Classification numbers for medical concepts and LCC numbers for non-medical concepts. The pertinent LCC schedules must be consulted since the numbers may change over time and are not automatically updated in the NLM Classification index.

Many headings are assigned a range of numbers rather than a specific number. The schedules of the NLM Classification or the LCC are the only source of the meaning of specific numbers within the range.

Example Index Page

The following is a screenshot of the online NLM Classification. This shows:

• MeSH Icon - Links the MeSH term in the Index to full descriptor data in the MeSH Browser (e.g., before Bronchial Neoplasms and Bronchial Provocation Tests).
• WF 500 - Links the Index headings to the appropriate classification numbers in the Schedules (e.g., WF 500 Bronchi).
• See also - Links to the related main index term or additional terms you may consider (e.g., Adenocarcinoma, Bronchiolo-Alveolar and Carcinoma, Bronchogenic).
• See - Cross-references within the Index to the preferred term, include Entry Terms from MeSH and non-MeSH references (e.g., Bronchopneumonia).
• + - Sub-Indexes (SIs) (e.g., Bronchial Provocation Tests)

Sub-Indexes (SIs)

Aspects of main index terms are entered in Sub-Indexes (SIs). By default, SIs associated with main index terms are collapsed, as shown in the example screenshot for Bronchial Provocation Tests above. SIs are expanded by clicking on the plus sign (+) in the online NLM Classification.

Sub-indexes may have several indentation levels, which further subdivide concepts.