Current Version - Under Revision
The content of SNOMED CT evolves with each release. The types of changes made include new Concepts, new Descriptions, new Relationships between Concepts and 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 CT users.
Once released, the unique Identifiers of SNOMED CT components are persistent, and their Identifiers are not reused. When a components becomes inactive this is indicated by the value of the active field, which is present in all components. Components continue to be distributed even when they are no longer active.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 components are 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 Sets are 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, Descriptions and Relationships.
Due to the origins of SNOMED CT, some SNOMED CT Concepts represent classification concepts that have imprecise and potentially changeable meanings. These are marked with the inactivation indicator value 900000000000486000 |limited|. These concepts were considered active until the January 2010 release of SNOMED CT. At that point, due to a change in editorial policy, this status was declared to be inactive.