As clinical practice evolves and adapts to meet the changing needs of healthcare, it is important that SNOMED CT reflects these changes, so that clinicians can adequately represent new and emerging techniques/practices. For any implementation of SNOMED CT it is therefore important to establish processes for end users and other stakeholders to submit requests for changes. Related to reference sets the types of changes that may be required include:

• Addition of new reference set members
• Removal of reference set members
• Changes to existing reference set members

Types of Refset Changes

Addition of new reference set members

When new members are requested for inclusion in a reference set, it should be determined whether any existing components in SNOMED CT are sufficient, or whether it requires a new component to be added - either in the International Edition or as part of an Extension.

Removal of reference set members (inactivation)

To remove a referenced component from a reference set, the relevant reference set member is inactivated. This is done by adding a new row to the reference set in which the value of the active column is set to false. The SNOMED CT versioning mechanism tracks the full history of additions, changes and inactivations because each row in the reference set contains a effective time column indicating when the change became effective. This is the same versioning mechanism with is used to track addition, inactivation and modification of SNOMED CT components.

Changes to existing reference set members

Changes to reference set members can vary, dependent on the refset type and the situation. Examples of changes include:

• Changing the order assigned to a member of an ordered reference set
• Changing the annotation associated to a member of an annotation reference set
• Changing a description from being acceptable to preferred in a language reference set
• Updating the query for an intensional subset definition represented by a member of a query specification reference set 

Approaches

The type of service implemented to support change requests will depend on the amount of reference sets, the number of users, the organisation etc.. Smaller organisations with relatively a few end-users may apply a simple email service for proposing any changes to the refset. Other institutions may implement dedicated systems that track each change request and support proper management of those.