Unified Medical Language System® (UMLS)

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  • Updated.jpg This entry is out of date, and will not be updated, February 2018


See also Data management portal | Families of Subheadings | FindZebra | Medical Subject Headings (MeSH) | National Library of Medicine (U.S.) | PubMed - MEDLINE

The Unified Medical Language System® (UMLS) is a compendium of ~150 controlled vocabularies created in 1986 for the biomedical sciences. The UMLS maps among these vocabularies and helps users to translate one ontology with another. The National Library of Medicine (U.S.) created the UMLS to provide a way to process natural language and across medical systems including electronic patient record companies. It potentially could play a role in developing the semantic web and in translating ontologies in a large framework. NLM produces the UMLS Knowledge Sources (databases) and software (programs) to retrieve, integrate and aggregate biomedical data. These sources are applied to a range of functions such as patient records, scientific literature, guidelines and public health information. New software tools assist developers in customizing knowledge sources; the lexical tools work most effectively with the Knowledge Sources but can be used independently.

What is a metathesarus?

A metathesaurus is a thesaurus of many thesauri organized by concept where each concept has specific attributes defining its meaning and is linked to the corresponding concepts in the various source vocabularies. A metathesaurus forms the basis of the UMLS and comprises 1 million biomedical concepts and 5 million concepts all of which derive from 150 incorporated controlled vocabularies and classification systems. Some examples are the ICD-10, Medical Subject Headings (MeSH), Systematized Nomenclature of Medicine-Clinical Terms (SNOMED CT), Diagnostic and Statistical Manual of Mental Disorders, LOINC, WHO Adverse Drug Reaction Terminology, UK Clinical Terms, RxNorm, Gene Ontology, and Online Mendelian Inheritance in Man (OMIM) (see full list).

Three (3) UMLS Knowledge Sources

All three sources are distributed with flexible tools and the MetamorphoSys installation program. For more information, see the NLM Factsheet - Unified Medical Language System and the NLM Technical Bulletin, Unified Medical Language System (UMLS) News http://www.nlm.nih.gov/pubs/techbull/ma10/ma10_umls_news.html.

What does UMLS contain?

  • ~150 controlled vocabularies in biomedicine
  • More than 2.1 million concepts and 9.8 million unique concept names
  • New sources:
  • Routine Health Outcomes (LNC_RHO)
CORE (Clinical Observations Recording and Encoding) Problem List Subset of SNOMED
  • New mapping file:
  • ICD10PCS_2009 to ICD9CM_2009 Mappings (Reimbursement)
  • Twenty-nine English sources and nine translation sources including MeSH®, MedDRA, RxNorm, and SNOMED CT (English and Spanish). For a list of updated sources, see the Updated Sources page. For detailed information on changes in this version of the Metathesaurus, see the Updated Sources (Expanded) Web page.
  • RxNorm data changes including adding the term type PIN (Precise Ingredient Name) and changes to the term type SY (Synonym)


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