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United States National Library of Medicine National Institutes of Health

Fact Sheet
UMLS® Metathesaurus ®

Introduction

The UMLS Metathesaurus is one of three knowledge sources developed and distributed by the National Library of Medicine as part of the Unified Medical Language System® (UMLS) project. The 2004AB Metathesaurus contains information about over 1 million biomedical concepts and 4.3 million concept names from more than 100 controlled vocabularies and classifications (some in multiple languages) used in patient records, administrative health data, bibliographic and full-text databases and expert systems. It includes vocabularies and coding systems designated as U.S. standards for the exchange of administrative and clinical data, including SNOMED CT® , LOINC® , and RxNorm.

Properties of the Metathesaurus

The Metathesaurus preserves the names, meanings, hierarchical contexts, attributes, and inter-term relationships present in its source vocabularies; adds certain basic information to each concept; and establishes new relationships between terms from different source vocabularies.

The scope of the Metathesaurus is determined by the combined scope of its source vocabularies. The Metathesaurus is produced by automated processing of machine-readable versions of its source vocabularies, followed by human review and editing by subject experts. The Metathesaurus is intended primarily for use by system developers, but can also be a useful reference tool for database builders, librarians, and other information professionals.

The Metathesaurus is organized by concept or meaning. Alternate names for the same concept (synonyms, lexical variants, and translations) are linked together. Each Metathesaurus concept has attributes that help to define its meaning, e.g., the semantic type(s) or categories to which it belongs, its position in the hierarchical contexts from various source vocabularies, and, for many concepts, a definition. A number of relationships between different concepts are represented. Some of these relationships are derived from the source vocabularies; others are created during the construction of the Metathesaurus. Most inter-concept relationships in the Metathesaurus link concepts that are similar along some dimension.

The Metathesaurus is a multi-purpose resource which must be customized for effective use in particular applications. At a minimum, most users will need to exclude vocabularies that are not relevant for specific purposes or not licensed for use in their institutions. MetamorphoSys, the multi-platform Java install and customization program distributed with the UMLS resources, helps users to generate pre-defined or custom subsets of the Metathesaurus.

Applying the Metathesaurus

The Metathesaurus supplies information that computer programs can use to create standard data, interpret user inquiries, interact with users to refine their questions, and convert the users' terms into the vocabulary used in relevant information sources. The Metathesaurus is used in a wide range of applications including: linking between different clinical or biomedical vocabularies; information retrieval from databases with human assigned subject index terms and from free-text information sources; linking patient records to related information in bibliographic, full-text, or factual databases; natural language processing and automated indexing research; and structured data entry. In many cases, the utility of the Metathesaurus is enhanced when it is used in combination with the SPECIALIST Lexicon, the lexical programs, and the UMLS Semantic Network. To obtain coherent, comparable results in data creation applications, such as patient data entry, it is necessary to define which Metathesaurus concepts and terms can be included in the records being created. This may be done by selecting one or more of the many Metathesaurus source vocabularies which provide the most appropriate concepts and terms for the specific data being created. Other Metathesaurus concepts and terms will then provide synonyms and related terms which can help to lead users to the vocabularies selected for a particular data creation application.

Obtaining the UMLS Metathesaurus

The Metathesaurus (and other UMLS products) is available free to both U.S. and international users. Users must complete an online Web-based License Agreement for the Use of UMLS Metathesaurus. Licensees are responsible for complying with the restrictions on use of the contents of the UMLS Metathesaurus that are detailed in the agreement. Although much of the content of the Metathesaurus may be used with minimal restrictions, some uses of some Metathesaurus source vocabularies require separate agreements, which may involve fees, with the individual vocabulary producers.

The UMLS Metathesaurus is available to licensees via download, by Web interface, and an applications programmer interface (API) from the UMLS Knowledge Source Server. It is also available on DVD to UMLS licensees by request. A complete description of the Knowledge Sources and their distribution formats can be found in the UMLS Documentation.

Other Fact Sheets in the UMLS series: Unified Medical Language System, UMLS Semantic Network , SPECIALIST Lexicon, UMLS Knowledge Source Server, and UMLS MetamorphoSys.

For additional information contact: E-mail: custserv@nlm.nih.gov or 1-888-FINDNLM

A complete list of NLM Fact Sheets is available at:
(alphabetical list) http://www.nlm.nih.gov/pubs/factsheets/factsheets.html
(subject list): http://www.nlm.nih.gov/pubs/factsheets/factsubj.html

Or write to:

FACT SHEETS
Office of Communications and Public Liaison
National Library of Medicine
8600 Rockville Pike
Bethesda, Maryland 20894

Phone: (301) 496-6308
Fax: (301) 496-4450
email: publicinfo@nlm.nih.gov

Last updated: 05 September 2004
First published: 01 January 1994
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