NLM® Classification Fundamentals

Classification (Class) Numbers

Class Number Format


Classification (class) numbers are alphabetical letters representing broad subject categories (schedules) which are subdivided by numbers.

Example

The following are example class numbers:

  • QT 25 would be for physiology (QT) laboratory manuals and technique (25).
  • WG 205 would be for resources on the cardiovascular system (WG) cardiac emergency treatment (205).

Spaces

There is a space between the letter(s) and the number(s) (e.g., QS 1 not QS1).

Example

Here are some examples using the QS and WA Schedules. Note that there is a space between QS and 1.


Examples of Spaces
Class Number Caption
QS
Human Anatomy
QS 1 Organizations. Societies (General or not elsewhere classified)
QS 4 General works
QS 5 Collected works by several authors
QS 7 Collected works by individual authors
QS 9 Addresses. Essays. Lectures
WA
Public Health
WA 1 Organizations. Societies (General or not elsewhere classified)
WA 4 Public Health
WA 5 Practice of Medicine
WA 7 Communicable Diseases
WA 9 Medicine in Selected Environments
WA 11 Musculoskeletal System
WA 11.1      General coverage (Not Table-G)
WA 13 Dictionaries. Encyclopedias
WA 15 Classification. Terminology

Decimals

Decimals further divide the class. It may or may not indicate subordinate class numbers.

Example

Class numbers WB 102.5 and WB 102.7 are subordinate to WB 102.


Examples of Decimals
Class Number Caption
WB
Practice of Medicine
Reference Works. General Works.
WB 102 Clinical medicine
WB 102.5      Evidence-based practice
WB 102.7      Genomic medicine. Precision medicine
WB 103 Behavioral medicine

Example

Class numbers WB 141.4 and WB 141.5 are not subordinate to WB 141.


Examples of Decimals
Class Number Caption
WB
Practice of Medicine
General Diagnosis
WB 141 General works
WB 141.4 Health status
WB 141.5 Differential diagnosis
WB 142 Prognosis. Monitoring

Indentation

Indented schedule captions always indicate class numbers for subordinate concepts.

Example

Class numbers WB 146–WB 182 are subordinate to WB 143.


Example of Indentation
Class Number Caption
WB
Practice of Medicine
Signs and Symptoms
WB 143 Signs and symptoms
WB 146      Fatigue. Sleepiness
WB 148      Asthenia. Cachexia. Wasting syndrome
WB 152      Chills. Fever
WB 158      Dehydration. Edema
WB 176      Pain
WB 182      Syncope. Coma

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