The design of SNOMED CT specifies that all components (concepts, descriptions and relationships) are identified usingSCTIDs. As extensions follow the logical design, content within an extension is also identified using SCTIDs. Another key requirement is that each SCTID is universally unique. This means that extensions need a mechanism to ensure their SCTIDs will not collide with the SCTIDs generated by other organizations or those generated by SNOMED International. This mechanism is called a SNOMED CTnamespace identifier. The namespace identifier ensures that all components within an extension are properly and uniquely identified.

Prior to creating an extension, each organization will need to obtain a unique namespace identifier from SNOMED International. Once the namespace identifier has been issued, SNOMED International authorizes the organization to generate SCTIDs within their allocated namespace. This means that organizations can create and maintain content in their own extension.

The allocated namespace identifier is 7 digits in length and is included in all SCTIDs within the extension. This ensures global uniqueness of SCTIDs across the terminology. Content in the International edition does not include a namespace identifier in the SCTID.

Examples

The table below lists some examples of namespace identifiers and the organizations they are affiliated with. These include National Release Centers (or NRCs), local organizations, and commercial vendors. Note that this table is an excerpt from the SNOMED CT Namespace Registry as of October, 2017.

 below uses the SCTID associated with the concept 5281000124103 |Persistent asthma| from the US edition of SNOMED CT, 20170301. Components of the SCTID have been labeled and the namespace identifier is shown in red. Note that the spaces do not form part of the SCTID and have been added to improve readability.

Caution

Example

Although 6811000087108 | CT guided biopsy of left lower limb|  includes the namespace identifier assigned to Canada Health Infoway, this concept is part of the | SNOMED CT core module|  in the International Edition. The presence of the Canadian namespace identifier along with a partition identifier of "10" in this SCTID likely indicates that this concept was promoted to the International Edition. Partition identifiers and promotion are discussed in subsequent sections.