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SNOMED CT FAQs

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.

SNOMED CT is a comprehensive clinical terminology that provides clinical content and expressivity for clinical documentation and reporting. SNOMED CT contains concepts for both human and non-human medicine and some of the covered domains are:

  • Clinical findings, including disorders,
  • Procedures, broadly defined as including all health related activities,
  • Observable entities which, when given a value, provide a specific finding or assertion about health related information.

The terminology is comprised of concepts; descriptions, which contain terms that explain the concepts; and relationships, which define the type of the association between two related concepts.

To learn more about SNOMED CT please see the IHTSDO SNOMED CT Starter Guide and the NLM SNOMED CT Overview.

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 US Edition of SNOMED CT is a standalone release file that combines the content of both the US Extension (US-specific content) and the International release of SNOMED CT.

The US Edition provides a single source of SNOMED CT content for use in the United States. For additional information regarding ONC Regulations please see the ONC FAQ.

SNOMED CT content is represented using three types of components supplemented by Reference Sets, which provide additional flexible features.

Concepts
CT concepts represent clinical thoughts, ranging from abscess to zygote. Every concept has a unique numeric concept identifier. Within each hierarchy, concepts are organized from the general to the more detailed. This allows detailed clinical data to be recorded and later accessed or aggregated at a more general level.

Descriptions
SNOMED CT descriptions link appropriate human readable terms to concepts. A concept can have several associated descriptions, each representing a synonym that describes the same clinical concept. Each translation of SNOMED CT includes an additional set of descriptions, which link terms in another language to the same SNOMED CT concepts.

Relationships
SNOMED CT relationships link concepts to other concepts whose meaning is related in some way. These relationships provide formal definitions and other properties of the concept.

Reference sets
Reference sets (Refsets) are a flexible standard approach used by SNOMED CT to support a variety of requirements for customization and enhancement of SNOMED CT. These include the representation of subsets, language preferences for use of particular terms and mapping from or to other code systems. Every reference set has a unique numeric concept identifier.

To learn more about SNOMED CT please see the IHTSDO SNOMED CT Starter Guide and the NLM SNOMED CT Overview.

The International Health Terminology Standards Development Organisation (IHTSDO) is an international not-for-profit organization based in London, UK. IHTSDO owns and administers the rights to SNOMED CT and related terminology standards.

The purpose of IHTSDO is to develop, maintain, promote and enable the uptake and correct use of its terminology products in health systems, services and products around the world, and undertake any or all activities incidental and conducive to achieving the purpose of the Association for the benefits of the members.

IHTSDO seeks to improve the health of humankind by fostering the development and use of suitable standardized clinical terminologies, notably SNOMED CT, in order to support safe, accurate, and effective exchange of clinical and related health information. The focus is on enabling the implementation of semantically accurate health records that are interoperable. Support to Association Members and Licensees is provided on a global basis allowing the pooling of resources to achieve shared benefits.

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 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. NLM also has representation on the Member Forum and on some of the IHTSDO Advisory Groups.

For additional information, please see the IHTSDO Governance and Advisory Webpage.

You can download the US Edition of SNOMED CT from NLM.

You will need to have signed a UMLS Metathesaurus license to access SNOMED CT from NLM. To request a license click "Sign Up" on the UTS Homepage. Additional information can be found on the UMLS License page and on the NLM SNOMED CT License page.

The UMLS Metathesaurus contains the complete US Edition 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.

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, such as 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.

NLM distributes the International Release of SNOMED CT files through the UMLS or as a standalone release file. The International Release of SNOMED CT web page lists all available files received from the IHTSDO.

Yes. The NLM 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.

You can download both the International Release and the U.S. Edition of SNOMED CT, as well as other SNOMED CT-related release files such as subsets and mapping files, through the NLM UMLS Terminology Services (UTS). You may also use the UMLS SNOMED CT Browser 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. A UMLS License is required to access and download SNOMED CT and to use the UMLS SNOMED CT Browser.

To request a license click "Sign Up" on the UTS Homepage. Additional information can be found on the UMLS License page and on the NLM SNOMED CT License page.

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, such as 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.

Release Format 2 (RF2) is the current release format developed by the International Health Terminology Standards Development Organisation (IHTSDO) to support the creation of reference sets. This has replaced Release Format 1 (RF1).

July 31, 2016 (International) and September 1, 2016 (US Edition) will be the last time SNOMED CT will be distributed in RF1. SNOMED CT will only be distributed in RF2 format. The key enhancements in RF2 are:

  • More robust and consistent version representation;
  • Reference sets, provides a more easily extensible and maintainable replacement for RF1 subsets and cross maps;
  • Use of an added hierarchy to represent metadata about the structure of SNOMED CT itself.

The RF2 release represents:

The components of SNOMED CT:

  • Concepts
  • Descriptions
  • Relationships

Additional derivatives that provide standard representations of:

  • Value-sets consisting of a specified set of concepts or relationships;
  • Cross mapping tables to other codes and classifications;
  • Support for extensions to the International Release using namespaces allocated to licensees to denote the provenance of added components and to ensure Identifier uniqueness.

The RF2 release file is provided in:

  • Tab-delimited text files;
  • Unicode UTF-8 specification.

Yes. The NLM 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.

The U.S. SNOMED CT Content Request System (USCRS) is available on the NLM SNOMED CT website. 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. Please see the NLM Learning Resources Database for tutorials on using USCRS.

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.

The IHTSDO and its members encourage the use of SNOMED CT in research that contributes to broadening our collective understanding and knowledgebase. Research projects may qualify for a free license if they:

  • Are supported by a formal proposal that has been peer reviewed,
  • Have been ethically approved in accordance with the prevailing legislation, regulations and guidelines in effect in the relevant territory,
  • Are conducted within a definite timeframe, and
  • The results of the research are offered for publication in peer-reviewed public journals and are provided to the IHTSDO free of charge.

To request a fee waiver, please contact the IHTSDO providing evidence that your research project meets the above criteria.

You must notify the IHTSDO of the use of SNOMED CT in any non-Member country. IHTSDO can be notified through its Member Licensing and Distribution Service (MLDS). More information can be found on the SNOMED CT and Licensing page. Please be aware fees may apply.

Additionally, if your registered office or principal place of business is in a Member country you must notify the Member for that country of your plans to use SNOMED CT in a non-Member country.

Which SNOMED CT files you use will depend on your usecase. The SNOMED CT is more than just a flat list of codes and more like a database. The content includes concepts, descriptions, and relationships.

When you unzip the US Edition of SNOMED CT you will find the Full, Snapshot and Delta versions. The Full release contains all of the SNOMED CT data from the beginning of SNOMED CT. It will include the full history of every single concept (when it was first introduced, if it has been edited, retired, etc.). The Snapshot version is a “snapshot” of the current SNOMED CT data. This release will provide information if the content (concepts, descriptions, and relationships) is currently active or retired. The Delta release contains the new/changed content for the current release.

Which files you need will really depend on your usecase. Are you using an electronic health record or system/application which was purchased from a vendor? If so, we suggest you contact your vendor so they can guide you as to which file(s) to use.

More information of the specific content of the different files can be found in the IHTSDO Technical Implementation Guide.

This depends on where you are planning to use SNOMED CT. If you plan to use SNOMED CT:

In the US

Licensees of the UMLS Metathesaurus have free access to SNOMED CT. The IHTSDO license terms for SNOMED CT cover use and distribution worldwide, but fees may be applicable outside IHTSDO Member countries.


Users should carefully read the license agreement before re-distributing any content in any type of application as there may be additional restrictions, permissions or copyright considerations imposed by the content providers. Users must contact the vocabulary content providers regarding any use that is not covered by the license. The content providers may charge fees for these additional uses of their content. Appendix 1 of the license agreement lists contact information for each content provider. The SNOMED CT® Affiliate License Agreement is included as Appendix 2 of the UMLS Metathesaurus License and outlines possible costs. NLM is a member of IHTSDO and there is no charge for SNOMED CT use in the United States and other Member territories. For information about fees in non-member countries, see the IHTSDO website.


To request a license click "Sign Up" on the UTS Homepage. Additional information can be found on the UMLS License page.


In another Member Territory

The UMLS is a global license and can be used to access SNOMED CT.

If you are planning to use, deploy or distribute SNOMED CT in a Member territory then the license can be obtained from that Member. The use of SNOMED CT in Member countries is free but we encurage you to check with the other Member's website to determine if there are other requirements. You can locate each Member country’s designated website by following the links from the IHTSDO website.


If you decide to use, deploy or distribute SNOMED CT in additional Member countries you should check the Member’s website to determine if there are requirements for use in that specific member country. Alternatively, you can also request a license from the IHTSDO.


As an alternative to obtaining the license from the Member, you may obtain the license directly from IHTSDO. However, you should check the Member’s website you plan to deploy or distribute SNOMED CT in to determine if there are any requirements for use in that specific country.


In a Non-Member Country

If you do not already hold a SNOMED CT license and you plan to use, deploy or distribute SNOMED CT only in a non-member country then you should apply for a license directly with IHTSDO. More information is available from the IHTSDO. Please be aware fees may apply.

The SNOMED CT Affiliate License is incorporated as Appendix Two in the UMLS Metathesaurus License.

If you decide to use, deploy or distribute SNOMED CT in additional Member countries you should check the Member countries’ website to determine if there are specific requirements for use in that specific Member country. You can locate each Member country’s designated website by following the links from the IHTSDO Members page.

There are no fees for SNOMED CT use in the US or other IHTSDO Member countries with a license but fees may be charged for use of SNOMED CT in non-member countries.

Fees are set and collected by the IHTSDO (owner organization of SNOMED CT). NLM cannot advise users on fees for specific projects. See the IHTSDO Web site for fee information and how to obtain a fee waiver for certain uses. You must contact the IHTSDO regarding a fee waiver BEFORE requesting a license from NLM.

No, an individual at the hospital/organization using your application/system must have a license as well. It is the same license for all users.

We do not offer a license for multiple users at this time. However, there is no limit on the number of individual licenses from an organization.

You need to notify and register your use with the IHTSDO BEFORE you use SNOMED CT in a Non-Member Country/Territory. You may register via the IHTSDO Member Licensing and Distribution Service (MLDS). Any additional questions should be directed to the IHTSDO.

Please contact NLM Customer Support for UMLS licensing questions or use of SNOMED CT in the US. For questions regarding use of SNOMED CT in non-Member territories or for fees please contact the IHTSDO.

The direction of the Map is from SNOMED CT (source) to ICD-10-CM (target). All pre-coordinated SNOMED CT concepts that are appropriate for use in a problem list (about a third of all active SNOMED CT concepts) are potentially within scope for the map. Initially, a smaller subset of frequently used SNOMED CT concepts will be mapped. Not all ICD-10-CM codes will appear as targets. Frequently occurring ICD-10-CM codes, within scope, are covered. Because of the difference in granularity of the two terminologies, some ICD-10-CM codes will not have SNOMED CT correspondents (e.g. concepts with laterality or episode of care information). Full representation of these ICD-10-CM codes will require post-coordination in SNOMED CT, which is not included in this Map.

The Map is intended to be used in a semi-automatic manner. The Map will suggest candidate ICD-10-CM codes based on SNOMED CT codes and, if applicable, additional information obtained from the electronic patient record or direct user input. Review of the candidate ICD-10-CM codes by either the healthcare provider or professional coder is recommended. The Map contains map rules and advice that can be used to highlight specific coding principles, or point to additional information required for coding. For the simple cases with one-to-one mappings, it is likely that a high proportion of the candidate ICD-10-CM codes will be adopted by the reviewer.

When a single SNOMED CT concept generates a combination of ICD-10-CM codes, the order of the ICD-10-CM codes complies with ICD-10-CM coding guidelines. For example, in a ‘dagger-and-asterisk’ (etiology and manifestation) code combination, the etiology code will be in Map group 1 and the manifestation code Map group 2. For injury or poisoning cases, the clinical condition code will be in Map group 1 and the external cause/poisoning code Map group 2. However, when a patient has multiple SNOMED CT-coded problems for a single encounter, each mapping to a different ICD-10-CM code, the Map does not include information to determine the order in which the ICD-10-CM codes should be submitted e.g. as primary or secondary diagnosis.

Not necessarily. In planning for the development of this map, advice was sought from the Center for Medicare and Medicaid Services (CMS) regarding ICD-10-CM code restrictions for reimbursement in the US. Due to regional variations in care profiles and carrier procedures for authorization of reimbursement, no authoritative resource could be identified to guide target code selection beyond those published by National Center for Health Statistics (NCHS).

No. The mappings are created to accurately reflect the meaning of the SNOMED CT concept. The level of reimbursement is not considered.