Executive Summary

SNOMED CT is a multilingual clinical terminology that covers a broad scope. However, some users may need additional concepts, relationships, descriptions or reference sets to support national, local or organizational needs. SNOMED CT is designed to allow the International Edition to be enhanced by creating extensions that meet national or local requirements. The extension mechanism allows SNOMED CT to be customized to address the terminology needs of a country or organization that are not met by the International Edition. An extension may contain components (i.e. concepts, descriptions or relationships) and/or reference sets used to represent subsets, maps or language preferences.

SNOMED CT extensions can support a variety of use cases, including:

• Translating SNOMED CT, for example

  • Adding terms used in a local language or dialect

  • Adding terms used by a specific user group, such as patient-friendly terms

• Configuring the terminology for specific use cases, for example

  • Specifying pick lists to be used for data entry

  • Specifying groups of components for reporting and analytics

• Managing content gaps, for example

  • Adding components that are missing in the

  • Adding concepts that are only relevant to a local context

• Mapping between SNOMED CT and other code systems, for example

  • Representing maps between SNOMED CT concepts and codes from other code systems

• Extending the expressivity of SNOMED CT, for example

  • Extending the concept model by introducing new attributes to meet specific data retrieval use cases

The logical design of a is technically consistent with that of the . Both represent and version SNOMED CT components and reference sets in release files that conform to the specification. Every includes one or more , and each contains either or (or both). A is published as a , which includes the contents of a focus module from the extension, together with the contents of all the modules on which it depends. This includes the modules in the and possibly other modules from a national and/or local extension. National and local are managed by or who have been issued a by . A is used to create globally unique for each (i.e. , and ) and reference set within a or . This ensures that references to extension contained in health record data are unambiguous and can be clearly attributed to a specific issuing organization. Once a has been obtained from , an extension producer must create one or more module concepts, which will be used to organize the extension content. All components and reference set members in an extension must belong to a module created by the responsible organization.

The key steps in producing a SNOMED CT extension are:

1. Planning - To ensure that the requirements can be met by the extension design, resources and processes that will be used.

2. Preparation - To ensure that the technical prerequisites are in place, including the namespace, modules, module dependencies and appropriate tooling.

3. Production - To develop, distribute and maintain the extension, including:

It is important for extension producers to understand the complexity of authoring and managing an extension, and to prioritize the acquisition of appropriate tools to support the extension management processes. These tools are required to maintain the quality and integrity of SNOMED CT content, and to prevent errors which can easily be identified using automated processes. Extensions and editions should never be handcrafted or managed manually using a file-based approach (e.g. using spreadsheets). While a manual approach may be possible in the short term (given a solid understanding of the principles), version management for an evolving extension can quickly become unsustainable over time. In addition, a lack of automated validation can have serious patient safety implications.