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NLM Classification 2016: Worldwide source of medical library classification

About the NLM Classification

Scope of Revision
Historical Development
Structure of the NLM Classification
Relationship to MeSH®

Scope of Revision

This edition incorporates all 2016 additions and changes to the schedules (see Class Numbers Added and Canceled) and to the index, which has been newly edited and updated with appropriate MeSH concepts. One hundred and thirty-nine (139) new index entries were created of which forty-two (42) are from the 2016 MeSH; the remainder are MeSH terms from previous years. Numerous main index entries and cross references were modified to reflect changes in the MeSH vocabulary. Seventy-eight (78) index entries were deleted.

Although the broad nature of the NLM Classification schedules precludes complete correspondence with MeSH, new class numbers were added and existing class numbers were canceled as needed to reflect other changes in MeSH and the biomedical and related sciences literature cataloged.

The QY (Clinical Pathology) and QZ (Pathology) schedules were the major area of focus for the 2016 edition.

The name of the QY schedule was changed from Clinical Pathology to Clinical Laboratory Pathology

Additions/changes were made to the QY schedule outline headers:

  • QY 50-110 Laboratory Animals. Laboratory Techniques was changed to QY 50-60 Laboratory Animals
  • QY 80-110 Laboratory Techniques was added
  • QY 120-350 Diagnostic Tests was changed to QY 118-350 Specimen Analysis. Diagnostic Tests
  • QY 400-490 Blood. Blood Chemistry was changed to QY 400-490 Hematologic Tests. Blood Chemical Analysis

Some QY class number captions and notes were revised to better reflect the scope of the number. For example:

  • At QY 25, the caption was changed from Laboratory manuals. Technique to Laboratory manuals (General).
    The note was changed from “Classify works on specific tests by type” to “Classify works on specific tests by type. Classify laboratory manuals on specific clinical techniques with the technique.”
  • At QY 50, the note was changed from “Classify works on diseases of laboratory animals in SF 996.5; on vivisection as experimental surgery in WO 50; and on antivivisection in HV 4905-4959” to “Classify here works on animals used in research, testing, or teaching, including their anatomy and diseases. Classify general works on animals in QL.”
  • At QY 58, the note was changed from “Cf. QY 25 Laboratory manuals” to “Classify works on experimental
    neoplasms in QZ 206.”
  • At QY 110, the caption was changed from Methods in medical mycology to Mycological techniques.
  • At QY 120, the caption was changed from Sputum to Sputum culture.
  • At QY 160, the caption was changed from Feces to Stool analysis.
  • At QY 265, the caption was changed from Agglutination, precipitation, flocculation, and complement fixation tests to Serologic tests (General).

Additions/changes were made to the QZ schedule outline headers:

  • QZ 40-109 Pathogenesis. Etiology was changed to QZ 40-105 Pathogenesis. Etiology
  • QZ 140-190 Manifestations of Disease was changed to QZ 140-190 Pathologic Processes
  • QZ 200-380 Neoplasms. Cysts was changed to QZ 200-380 Neoplasms
  • QZ 310-380 Specific Types of Neoplasms was added

Some QZ class number captions and notes were revised to better reflect the scope of the number. For example:

  • At QZ 4, the note was changed from “Classify material on comparative pathology in QZ 33” to “Classify works on both the specialty and pathologic processes here. Classify works on the specialty only in QZ 21. Classify works on pathologic processes only in QZ 140. Classify material on comparative pathology in QZ 33.”
  • At QZ 52, the caption was changed from Genetic testing to Genetic services.
  • At QZ 140, the caption was changed from General manifestations of disease to Pathologic processes (General).
  • At QZ 150, the caption was changed from Local reactions to injury and disease to Inflammation.
  • At QZ 201, the note was changed from “Classify here popular works on all aspects of neoplasms” to “Classify here popular works on neoplasms in general. Classify popular works on neoplasms by site in the appropriate schedule.”
  • At QZ 206, the caption was changed from Research (General) to Research (General). Experimental neoplasms. The note was changed from “Classify works on specific topics by subject, e.g., on experimental work on the etiology of neoplasms in QZ 202” to “Classify here all works on experimental neoplasms regardless of type or site.”

Changes were made to other class schedules. For example:

  • At QS 26, the note was changed from “Classify catalogs here” to “Classify catalogs here. Classify here all works on physical anatomic models even if used for educational purposes. Classify digital anatomic models in QS 26.5. Classify works on use of anatomic models for special subjects by subject.”
  • At WC 160, the note was added: “Classify works on syphilis serodiagnosis in QY 275.”
  • At WH 250, the note was deleted: “Classify works on histology and pathology of leukemia in QZ 350.”
  • At WI 950, the note was added: “Classify works on hernias in general in QZ 140.”
  • Surveys was added to the caption of form number 16 in most schedules. Form number 16 now allows for Table G breakdown.
  • The form number for individual museums and exhibitions in each schedule now allows for Table G breakdown.

A systematic review was conducted of the Table G (Geographic Notations). As a result:

Changes to the Current Section:


  • GK6--Kosovo
  • HS07--Sao Tome and Principe
  • HS7--South Sudan


  • DS2--Salvador changed to El Salvador
  • FG9--Guernsey changed to Channel Islands
  • HC4--Cape Verde Islands changed to Cabo Verde
  • LE1--East Timor changed to Timor-Leste
  • PA6--Antarctic changed to Antarctic Regions
  • PA7--Arctic changed to Arctic Regions

Additions to the Historical Geographic Locations:

  • GG4--East Germany
  • GG4--West Germany
  • JB9--Byzantium
  • JI7--Persia
  • JM4--Mesopotamia
  • LP2--New Guinea
  • JP2--Palestine (formerly in the Middle East and Asia section)

Some cross references were added, e.g., Mekong Valley see Southeastern Asia. Several cross references were deleted because they were duplicative of MeSH cross references, e.g, Basutoland see Lesotho.

Historical Development

The genesis of the NLM Classification is a Survey Report on the Army Medical Library, published in 1944, which recommended that the "Library be reclassified according to a modern scheme," and that the new scheme be a mixed notation (letters and numbers) resembling that of the Library of Congress. Subsequently a classification committee was formed, chaired by Keyes D. Metcalf and including Mary Louise Marshall who compiled the schedules. Medical specialists acted as consultants to the committee. Based on the consultants' advice, that of the committee and of the NLM cataloging staff, Ms. Marshall produced a preliminary edition of the Library's Classification, which was issued in 1948.

The preliminary edition was revised by Frank B. Rogers and the first edition of the new classification was published in 1951 as the U.S. Army Medical Library Classification. It firmly established the current structure of the classification and NLM's classification practices. The headings for the individual schedules were given in brief form (e.g., WE - Musculoskeletal System; WG - Cardiovascular System) and together they provided an outline of the subjects that constitute the National Library of Medicine Classification . These headings were interpreted broadly as including the physiological system, the specialty or specialties connected with them, the regions of the body chiefly concerned and subordinate related fields. Within each schedule, division by organ usually has priority. All schedules, including some of their sections, are preceded by a group of form numbers representing publication types. These numbers, ranging generally from 1-39, are employed as mnemonic devices throughout the Classification.

Beginning with the 2002 edition, the National Library of Medicine Classification is published in electronic form and updated annually:

The online environment offers many advantages to users including hyperlinks between class numbers in the index and the schedules, and between terms within the index and direct links from these to the MeSH record itself under the MeSH Browser.

The online data creation and maintenance system of the Classification gives NLM the ability to update the classification annually in tandem with MeSH. Publication of printed editions ceased with the 5th revised edition, 1999. Beginning with the 2006 edition, the NLM Classification is also available in PDF (Portable Document Format) at

Structure of the NLM Classification

The National Library of Medicine Classification covers the field of medicine and related sciences, utilizing schedules QS-QZ and W-WZ, permanently excluded from the Library of Congress (LC) Classification schedules. The various schedules of the LC Classification supplement the NLM Classification for subjects bordering on medicine and for general reference materials. The LC schedules for Human Anatomy (QM), Microbiology (QR) and Medicine (R) are not used at all by the National Library of Medicine since they overlap the NLM Classification.

Relationship to MeSH

The schedules, with their special requirements for use with all types and forms of materials, preclude strict adherence to the hierarchical arrangement of the Medical Subject Headings (MeSH), the Library's thesaurus for indexing and cataloging. The schedules maintain their own character in order to provide for material, old as well as new, acquired for the Collection, including dictionaries, atlases, directories and other items, which are not suitable for the arrangements, found in MeSH. However, an effort was made to make schedule headings, subheadings and class number captions compatible with MeSH terminology. The MeSH Tree Structures were used extensively to determine the proper placement of a concept in a schedule and to relate index headings to one another. Since the representation of subjects in the schedules of the NLM Classification is intentionally broad, the captions do not enumerate all of the subordinate concepts that are to be classified in a given number. MeSH descriptors for these subordinate concepts do appear in the index, to the extent practical with appropriate references to the classification numbers.


The Index to the NLM Classification consists primarily of Medical Subject Heading (MeSH) concepts used in cataloging. It includes concepts first appearing in the latest edition of MeSH and other older concepts as warranted by the literature cataloged. It also provides access to classification numbers through these MeSH concepts. Index entries are updated annually to reflect additions and changes of the latest edition of MeSH. For additional information on the Index see About the Index.