Skip Navigation Bar

Unified Medical Language System® (UMLS®)

FAQs: SNOMED CT® in the UMLS®  


  1. Q. What is SNOMED Clinical Terms (SNOMED CT)?

    A. SNOMED CT is an extensive clinical terminology that was formed by the merger, expansion, and restructuring of SNOMED RT® (Reference Terminology) and the United Kingdom National Health Service (NHS) Clinical Terms (also known as the Read Codes). It is the most comprehensive clinical vocabulary available in English (or any language). SNOMED CT is concept-oriented and has an advanced structure that meets most accepted criteria for a well-formed, machine-readable terminology. It has been designated as a US standard for electronic health information exchange in Interoperability Specifications produced by the Healthcare Information Technology Standards Panel and has also been adopted for use by the US Federal Government, through the Consolidated Health Informatics (CHI) Initiative, for several clinical domains.
  2. Q. Who owns SNOMED CT?

    A. SNOMED CT was acquired in April 2007 by the International Health Terminology Standards Organisation (IHTSDO). The IHTSDO purchased the intellectual property of SNOMED CT and antecedent works from the College of American Pathologists (CAP), which created and maintained it for more than 40 years. The goal of the change in ownership was to promote international adoption and use of SNOMED CT. The IHTSDO is responsible for ongoing maintenance, development, quality assurance, and distribution of SNOMED CT. The CAP will continue to support SDO operations under contract and to provide SNOMED CT-related products and services as a licensee of the terminology.
  3. Q.How is the US represented in the international organization that owns SNOMED CT?

    A. NLM is the US Member of the IHTSDO - one of the nine original Charter Members. As an IHTSDO member, NLM has rights and responsibilities that include the distribution of SNOMED CT (both English and Spanish versions) in multiple formats. Details are available in the IHTSDO Articles of Association. NLM supports this effort through a contract with the IHTSDO under which NLM pays an annual fee (approximately $6 million per year) to make SNOMED CT available free of charge to anyone in the US.

    NLM is a voting member of the General Assembly of the IHTSDO and serves as a focal point for US input to the ongoing development of the terminology. The US is currently represented on the IHTSDO Management Board by Andrew Wiesenthal, MD, SM. Permanent executive officers have been appointed including Kent Spackman, MD, Oregon Health Sciences University, as the Chief Terminologist.

    The IHTSDO has four standing Committees: Content, Implementation & Innovation, Quality Assurance, and Technical. Potential committee members are nominated by each member country and voted on by the IHTSDO’s General Assembly. NLM coordinates the committee nominations for the US.  SNOMED CT users may also volunteer for various Working Groups (includes Special Interest Groups and Project Groups). Interested parties should contact NLM Customer Service for more details.

    NLM has developed the U.S. SNOMED CT Content Request System (USCRS), s Web-based application for use in the US. See Question 11 for more information.
  4. Q. What impact did the 2007 change in SNOMED CT ownership have on existing UMLS Licensees?

    A. In 2007 UMLS licensees were required to review and accept a revised License Agreement for Use of the UMLS Metathesaurus, which now incorporates the uniform international IHTSDO Affiliate License.

    In addition to access to the International Release of SNOMED CT within the UMLS Metathesaurus, UMLS licensees also have free access from NLM to SNOMED CT in its native file formats, to the documentation supporting these files, and to a growing set of subsets and mapping files.

    UMLS licensees have broader rights to create and distribute SNOMED CT extensions and derivative works under the uniform international IHTSDO Affiliate License that is now part of the UMLS License. The license covers all types of use in all countries. Fees apply to some types of distribution or use in countries that are not yet Members of the IHTSDO.
  5. Q. What SNOMED CT content is in the UMLS Metathesaurus?

    A. The UMLS Metathesaurus contains the complete International Release of SNOMED CT in English and Spanish. For the specific versions that are included in each edition of the UMLS Metathesaurus, consult the documentation for that edition.
  6. Q. How is SNOMED CT represented in the UMLS Metathesaurus?

    A. The UMLS Metathesaurus includes many different vocabularies in a common, explicit, concept-based format. SNOMED CT has been converted to the common UMLS format, its concept names have been connected to those already in the Metathesaurus, and its content has been assigned UMLS identifiers, semantic types, etc. See Explanatory Notes for additional details, including a mapping between SNOMED CT ’s tables and fields and the tables and fields in the Metathesaurus.
  7. Q. How can I extract SNOMED CT from the UMLS Metathesaurus and browse it?

    A. MetamorphoSys, free Java software, is distributed with the UMLS to assist users in producing subsets of the Metathesaurus. It includes some predefined filters for generating subsets that include SNOMED CT. Users are able to modify filters and defaults to generate a desired subset of the Metathesaurus, or write their own custom filters. Any output from MetamorphoSys includes some basic UMLS Metathesaurus data, e.g., NLM Concept Unique Identifiers (CUIs) as well as Lexical Unique Identifiers (LUIs), and String Unique Identifiers, SUIs). The UMLS RRF Browser, also free Java software distributed with the UMLS content, allows users to browse any subset output by MetamorphoSys.
  8. Q. Where can I read more about the UMLS, the current file formats, the sources included, etc.?

    A. Complete details about the UMLS are available from the UMLS home page. The current UMLS license, which includes an appendix that lists all vocabularies currently in the Metathesaurus and the IHTSDO Affiliate license for use of SNOMED CT, is available here.
  9. Q. Where can I get the International Release of SNOMED CT in its native file format?

    A. NLM distributes the International Release of SNOMED CT files through the UMLS. The SNOMED CT Release Files web page lists all available files received from the IHTSDO.
  10. Q. Is there a SNOMED CT Browser available?

    A. Yes. NLM's SNOMED CT Browser is available through the UMLS Terminology Services (UTS). The SNOMED CT Browser enables users to search for and display SNOMED CT content, as included in the UMLS Metathesaurus. The search mechanism uses UMLS data and tools to enhance the retrieval.

    NLM has also created the SNOMED CT Browsers page listing browsers mentioned in IHTSDO forums and relevant literature. The list is solely provided as an added resource and is not meant to be a comprehensive list of all SNOMED CT browsers.
  11. Q. How can I submit content that does not appear in SNOMED CT to be reviewed for inclusion?

    A. The U.S. SNOMED CT Content Request System (USCRS) is available on the NLM Web site.  You must be a UMLS licensee (SNOMED CT Affiliate) and use your UTS  account to sign in.  You may enter requests online, or download the USCRS batch template spreadsheet from the "Resources" menu and prepare them offline.  You may also search and view requests in the system, and track them as they move through the workflow from evaluation to inclusion (if accepted) in either SNOMED CT International or the US Extension.

    An understanding of SNOMED CT content and structure is required to create successful requests. Each request must include a SNOMED CT identifier that links to an existing concept in either SNOMED CT or the US Extension. Every request must also provide a justification or practical use case.