Value set authors should create value sets with the thoughtful input of subject matter experts familiar with the clinical or administrative information needed, combined with the input of terminology experts familiar with the code systems used. This work requires strong knowledge of current information capture (both electronic encoding and traditional textual material) and the workflow necessary to capture the expected information accurately.
Representing the Codes for Inclusion
When constructing a value set, the value set author is actually constructing a value set definition (VSD) that may have multiple versions over time. A VSD describes the value set using metadata and includes a Content Logical Definition (CLD) that identifies the specific concepts (i.e., codes) for inclusion in the value set expansion. An expansion profile is a set of rules defined by a particular program, for example, the “eCQM Update 2022-05-05” expansion profile applied a set of allowable code system versions, defined by CMS. An additional rule in the expansion profile determines if the expansion will include concepts specified in the CLD that are inactive in the code system version used for the expansion. In the Value Set Authority Center (VSAC), a download of the value set expansion will include the concept code, text display (description), the code system name, identifier, and the code system version used for each member in the expansion set.
Many constructed VSDs enumerate each desired specific code, traditionally called an enumerated or extensional definition. However, the best definition of many value sets is logically or intensionally using the structure of the specific code system (e.g., all the codes that are descendants of the condition Insulin Dependent Diabetes Mellitus). For example, "include all concepts that are children of a parent concept" in a hierarchical code system.
A simple enumeration of concepts is not always an ideal approach to define a value set. A comprehensive approach to quality measure development entails examination of complete code hierarchies in a code system to determine the levels of concept inclusion. The VSAC provides tooling to support both extensional and intensional VSDs.
Value Set Versioning
The value set author creates the value set definition to specify the value set content. The value set steward reviews and passes the value set definition and then publishes the value set definition. VSAC gives it a version identifier, known as “the value set definition version.”
A value set definition version update occurs whenever the steward publishes a new version. Possible reasons for a new version are when there is a change in the value set’s defined codes, grouping member value sets, or algorithmic logic (intensional).
When there is an expansion of a published value set definition, the result is a “value set expansion version.” The VSAC always makes available for use by value set users an expansion based on the current published value set definition version. That expansion version has the string identifier of “Latest” and the expansion content in Latest will change if the current value set definition changes to a new version and/or the code system version changes in a way to affect the constituent concepts.
Including Historical Codes
Some value sets may need to include concepts that are no longer active concepts in the code system of choice. This usually occurs when a measure clause includes a value set that requires a look-back period that extends back more than a year or the length of time between code system updates, due to the fact that the entry of the newly retired codes into patient records occurred when they were still active codes. No value set author should expect owners of old patient records will update content to use current codes. Therefore, value sets for use to identify patients based on old record content may need to include inactive legacy codes in the value set expansions. Value set authors should document the need for including retired codes in the purpose statements of the value set metadata section. Value set authors that need historical codes in an expansion must include those codes within the CLD of the value set and confirm that the expansion profile used for the specified eCQM program release sets the "Legacy/Retired Codes" rule to apply the most recent code system version that includes the code in an active status.