Back to top

Value Set Information

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], 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).


  • 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:


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.


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.


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.

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, and a set of desired legacy codes, approved by CMS. 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 need to notify VSAC about any retired codes they need to use in a value set. (See the Updating Value Sets section of the VSAC Support Center.) VSAC will then include the value set author’s specified retired codes as legacy codes within the expansion profile calculation applied to the specified electronic clinical quality measure program release.

This guidance is intended for value set authors. The guidance provides direction on the best practices for authoring and maintaining value sets for quality measures, electronic clinical quality improvement, and other applications.

CMS requires their contracted measure developers to follow this guidance unless otherwise stated in the contract or by their Contracting Officer’s Representative. CMS and other Health and Human Services agencies recommend other measure developers and authors of value sets follow these guidelines and principles for value set development and maintenance.

This value set guidance provides best practices in value set naming, descriptions, and maintenance.

Last Updated: Apr 17, 2023