Overview

What is MeSH?

Medical Subject Headings (MeSH) is an internationally employed controlled vocabulary thesaurus constructed by the National Library of Medicine (NLM). It is used for cataloging, indexing, and searching medical and health related topics on NLM databases. MEDLINE/PubMed® is perhaps the most widely known NLM database. There are many online sources that provide free access to MeSH, including the NLM website.

How is MeSH constructed?

MeSH is organized using a hierarchical tree structure, using 16 lettered base terms. These base terms are listed below. The 16 main categories are further divided into subcategories, increasing in specificity as the searcher proceeds down the tree ‘branch.’ There are up to 11 hierarchical levels for each main branch. Each level is numbered to indicate its place in the tree. The numbers are subject to change when new descriptors are added or the vocabulary changes. Terms located at the same level of specificity are listed in alphabetical order.

1. Anatomy (A)
2. Organisms (B)
3. Diseases (C)
4. Chemicals and Drugs (D)
5. Analytical, Diagnostic and Therapeutic Techniques and Equipment (E)
6. Psychiatry and Psychology (F)
7. Biological Sciences (G)
8. Natural Sciences (H)
9. Anthropology, Education, Sociology and Social Phenomena (I)
10. Technology, Industry, Agriculture (J)
11. Humanities (K)
12. Information Science (L)
13. Named Groups (M)
14. Health Care (N)
15. Publication Characteristics (V)
16. Geographicals (Z)

Following is a visual representation directly from MeSH. It is the first entry under the first category, ‘anatomy.’

Body Regions [A01]

• Abdomen [A01.047]
  • Abdominal Cavity [A01.047.025]
    • Peritoneum [A01.047.025.600]
      • Douglas’ Pouch [A01.047.025.600.225]
      • Mesentery [A01.047.025.600.451]
        • Mesocolon [A01.047.025.600.451.535]
      • Omentum [A01.047.025.600.573]
      • Peritoneal Cavity [A01.047.025.600.678]
      • Peritoneal Stomata [A01.047.025.600.700]
    • Retroperitoneal Space [A01.047.025.750]
  • Abdominal Wall [A01.047.050]
  • Groin [A01.047.365]
  • Inguinal Canal [A01.047.412]
  • Umbilicus [A01.047.849]

Retrieved from http://www.nlm.nih.gov/mesh/trees2008/A01.html, 31 January 2008

The MeSH tree structure is comprised of three basic components:

• Descriptors
• Qualifiers
• Supplementary Concept Records (SCRs)

Descriptors are also called Main Headings (MH). Most refer to the subject of the package of information. These descriptors are updated on an annual basis. In the 2008 MeSH, there are nearly 25,000 Descriptors.

Qualifiers are also called Subheadings (SH), used to focus MH. There are 83 Qualifiers in MeSH. Qualifiers are also updated annually. Qualifiers function to group together similar aspects of a subject, or Descriptor. Not all Qualifiers are applicable to every Descriptor.

For example, the third Qualifier in the list of 83 is ‘adverse effects.’ This Qualifier would be relevant to use when cataloging the main branches Organisms (A), Chemicals and Drugs (D), Analytical, Diagnostic and Therapeutic Techniques and Equipment (E), and Technology, Industry, Agriculture (J). ‘Adverse effects’ would not be a Qualifier used in say, Humanities (K).

MeSH also uses See references. See related is used to cross-reference Descriptors. Consider also is used to reference terms with related linguistic roots.

See from references are used when a search term is unauthorized. The reference gives designators such as narrower term (NT) or broader term (BT) and points to the appropriate authorized term. Searchers will also be automatically alerted when they attempt a term that is more precisely cataloged in the literature.

SCRs are used to index substance names (i.e. drugs, chemicals). SCRs do not have numbers, but are rather linked to Descriptors from a separate thesaurus. MeSH currently has over 172,000 SCR headings. SCRs are updated weekly.