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Current Version - Under Revision

The content of SNOMED CTevolves with each release. The types of changes made include new Concepts, new Descriptions, new Relationshipsbetween Conceptsand new Reference Sets, as well as updates and retirement of any of these components. Drivers of these changes include changes in understanding of health and disease processes; introduction of new drugs, investigations, therapies and procedures; and new threats to health, as well as proposals and work provided by SNOMED CTusers.

Once released, the unique Identifiersof SNOMED CT componentsare persistent, and their Identifiersare not reused. When a componentsbecomes inactive this is indicated by the value of the active field, which is present in all components. Componentscontinue to be distributed even when they are no longer active. This allows a current release to be used to interpret data entered using an earlier release.

Since the implementation of Release Format 2(RF2), all changes in componentsare represented in the corresponding files, by adding a new row, with the same component ID, a new effective time and any necessary change in the component values.

The Component Inactivation Reference Setsare used to indicate the reason for inactivating a component. These reasons include errors, duplication of another component and ambiguity of meaning, and the files are used to describe reasons for inactivation of Concepts, Descriptionsand Relationships.

Due to the origins of SNOMED CT, some SNOMED CT Conceptsrepresent classification conceptsthat have imprecise and potentially changeable meanings. These are marked with the inactivation indicator value 900000000000486000 |limited|. These conceptswere considered activeuntil the January 2010 release of SNOMED CT. At that point, due to a change in editorial policy, this status was declared to be inactive.

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