Purpose

SNOMED CT is a multilingual clinical terminology that covers a broad scope of clinical concepts to an appropriate level of detail for international use. In addition, it provides an extension mechanism that allows SNOMED CT to be customized to address terminology needs that are not met by the International Edition. This mechanism enables new concepts, relationships, descriptions and reference sets to be added to support national or local needs.

However, not every new terminology requirement requires a SNOMED CT extension to be created. Potential extension producers should be aware of situations in which it is beneficial to create an extension, and situations where alternatives may be preferable. The following table provides a summary.

Create an extension when ...	An extension is not required when ...
New national or local content is required to meet usage requirements; or The content of the extension needs to be shared with other organizations; or The standard file format and versioning mechanism of the release format 2 is needed	No new national or local content is required: and The content of the extension does not need to be shared with other organizations; and Non-standard formats are sufficient to support local requirements.

When a SNOMED CT extension is required, the extension may serve a range of purposes. Successful extension producers must clearly understand the requirements and purpose of their extension, before deciding which types of SNOMED CT artifacts should be included.

Table below shows some typical purposes for a SNOMED CT extensions. For each purpose, the table includes some common use case examples and a list of SNOMED CT artifacts that should be included. For more information about each of these purposes, please click on the corresponding diagram.

Table: Purposes and use cases for extensions

Purpose	Use Case Examples	Included Artifacts
Translate SNOMED CT	Adding terms used in a local language or dialect Adding terms used by a specific user group, such as patient friendly terms	Descriptions Language reference sets Concepts (metadata only) Relationships (metadata only)
Manage content gaps	Adding components that are missing in the International Edition Adding concepts that are only relevant to a local context	Concepts Descriptions Relationships Language reference sets
Maps between SNOMED CT and other code systems	Maps between local codes and SNOMED CT Maps between statistical classification systems and SNOMED CT	Map reference sets Concepts (metadata only) Descriptions (metadata only) Relationships (metadata only)
Configuration of the terminology for specific use cases	Specifying groups of components for reporting and analytics Linking components to clinical knowledge resources	Reference sets Concepts (metadata only) Descriptions (metadata only) Relationships (metadata only)

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