Value sets are a subset of concepts (each concept represented by a code) drawn from one or more code systems, where the concepts included in the subset share a common scope of use. The codes and corresponding terms come from standard clinical vocabularies (such as Current Procedural Terminology [CPT], Systematized Nomenclature of Medicine Clinical Terms [SNOMED CT], RxNorm, and Logical Observation Identifiers Names and Codes [LOINC]) and define clinical concepts to support effective and interoperable health information exchange. Value set authors use value sets in quality measures and clinical decision support to collect all the coded concepts that can occur in the clinical record (or administrative data), represent patients or encounters that should be in the same population for analysis, and provide condition-specific diagnostic support and order sets.
Value sets have a life cycle similar to many persistent objects. The Value Set Authority Center (VSAC) is a tool suite developed by the National Library of Medicine to support the creation, maintenance, and retrieval of value sets. The VSAC serves as the central repository for the CMS electronic clinical quality measure value sets. However, other value set repositories are available, such as the Public Health Information Vocabulary Access and Distribution System.
The VSAC Support Center provides online information about VSAC access, value set lifecycles and workflow, measure developer and steward roles, and best practices for value set development. In addition, the VSAC Support Center offers archived users’ forums and release notes and provides links to VSAC publications.
Coded Data Elements
Coded data elements in quality measures are bound to (i.e., may use) either
- A single specific code (drawn from a code system) directly referenced within the measure and, as such, is not a value set; therefore, it is a direct reference code (DRC).
OR
- A value set (i.e., a set of codes) where each code is equivalent with respect to use in the context of that data element.
In quality measures, the patients or encounters identified using any of the codes in a value set are equivalent with respect to the measure data element using the value set.
Value Set Creation Methods
In VSAC, a value set contains specific codes derived from a single code system or vocabulary. Value set users refer to codes and their descriptions as concepts in VSAC, value set authors can group value sets to combine code systems. Value set authors can create value sets using several methods:
Extensional:
A set of concept codes and descriptors in the form of an enumerated list. An extensional value set in the VSAC contains codes from only one code system.
Intensional:
A list of codes based on a logical statement that often has an algorithmic basis for the selection of concepts based on concept properties or relationships as defined within the code system. An intensional value set in the VSAC contains codes from only one code system.
Grouping:
A collection of one or more value sets that, when combined, meet the requirements of the grouping value set purpose. Value set authors often use grouping value sets in the VSAC to combine member value sets from different code systems so the grouping value set expansion set includes concepts from multiple code systems. In VSAC, grouping value sets cannot group other grouping value sets.