NLM Classification Fundamentals

Finding the Appropriate Class Number

Concepts

Specific

In the NLM Classification Index, some subjects may be indexed to a specific number (Note: these one-to-one class numbers may also be visible in the MeSH Browser, but the schedules should still be checked).

Always refer to the main schedule to verify the number to be certain there are no annotations directing the cataloger to use another number in specific circumstances.

Example

The NLM Classification Index entry for "Reticulocytes" links to WH 150 in the schedule, which is the broader concept "Erythrocytes."

Screenshot of Reticulocytes from NLM Classification Index — Screenshot of "Reticulocytes" from NLM Classification Index

WH 150 in the NLM Classification Schedule
Class Number	Caption
WH Hemic and Lymphatic Systems Hematologic Diseases. Hematopoietic System
WH 150	Erythrocytes

General

Some subjects may include a range of numbers. Refer to the section of the class schedule to which the primary subject is indexed and select the most appropriate number.

Example

The NLM Classification Index entry for "Acquired Immunodeficiency Syndrome" links to 503-WC 503.8 in the schedule. This includes more than what is listed underneath the entry in the index.

Screenshot of Acquired Immunodeficiency Syndrome from NLM Classification Index — Screenshot of "Acquired Immunodeficiency Syndrome" from NLM Classification Index

Select the class number annotated "General Works" if the subject is very general or if the primary focus of the work includes several subjects within the schedule.