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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:

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.

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.

Value Set Naming Best Practices

Value Set Name	Guidance
Limit the value set name to as few words as possible and no more than 128 characters.	Create a short, descriptive, user-friendly title for the value set. Avoid a long description yet capture critical, distinctive aspects of the membership criteria.
Create the value set name to convey the specific distinguishing characteristics of the member concepts.	Use a sufficiently descriptive name. The value set name "Diabetes" is not sufficiently descriptive if it only contains codes describing Type II diabetes. The value set name "Diabetes Type II" is a better name because it more effectively describes the scope of the value set. Avoid including descriptions of the intended, but not achieved, content.
Make value set names unique.	Use a sufficiently descriptive name. Best practice discourages use of duplicate value set names and should be uncommon. Grouping value sets may have member value sets with the same name, as these members often have the same purpose, yet their content is differentiated by specific code system content. Value sets with different metadata (purpose, intent, inclusion, and exclusion statements) should always have names reflective of the metadata and therefore should have a unique name.
Use correct spelling and grammar.	Separate multi-word terms by spaces and not by any other characters. Use title case (capitalize first letters of all words, except prepositions, as in a title). Do not include "camelCase," composite, or delimited words or phrases.
Avoid these items in a value set name	The Value Set Authority Center (VSAC) prohibits certain characters (+ * ? : -\| ! " %) and provides a system warning if used. Value set steward name – The VSAC database captures the steward’s name in a separate field in the metadata, which is bound to the value set. Name of the specific data element the value set was created to support. Do not include the concept category that characterizes the context of use, unless it describes a primary distinguishing characteristic of the value set requirements. For example, only include the word “Procedure” when the context of the focus is ambiguous. Appropriate Name – Insulin Dependent Diabetes Diagnoses Inappropriate Name – Diabetes Condition, Diagnosis, or Health Concern Appropriate Name – Mobility-Related Health Concerns Inappropriate Name – Mobility Health Concerns Quality reporting program name unless it describes a primary distinguishing characteristic of the value set. Names of measure types or settings (e.g., hospital measures, process measures). Code descriptors within the value set name. Abbreviations unless widely used in the medical literature, e.g., HIV.
Never use the word “other” as an alternative to another value set.	For example, do not name a value set "Other Endophthalmitis" just because a value set named "Purulent Endophthalmitis" already exists. Be as specific as possible. "Other Endophthalmitis" lacks adequate information value set users need. Non-purulent Endophthalmitis could be a better name to indicate another type of Endophthalmitis.
Renaming	Rename a published value set to add clarity to the name and update the version of the value set. If there is a change to the description, intent, or content, consider the need to create a new value set. Correct the name if not able to align the value set content with the initial name given to the value set. For example, if initially named "Oral Anticoagulants" when the intent was to capture only oral anticoagulants for chronic atrial fibrillation, change the name to "Oral Anticoagulants for Chronic Atrial Fibrillation" to align it with the intended purpose.

Value Set Description Best Practices

High-quality value sets provide a clear and comprehensive description of the constituent concepts of the value set including the intent or use of the value set. In the VSAC, a purpose statement has four components (clinical focus, data element scope, inclusion, and exclusion criteria) to provide information a value set user can use to understand the content, the use of the value set, and the scope or breadth of concepts for inclusion or exclusion in the value set. Currently, the VSAC does not require a purpose statement to publish a value set, however, it is best practice to include a purpose statement with all four components completed for a published value set.

If the value set author meaningfully changes the focus or intent of the value set, the value set author should evaluate for continued appropriateness as fit for purpose. If not found consistent with the original focus or intent, the value set author should consider creating a new value set.

Purpose Statement Component	Guidance
Clinical Focus	Clinical Focus is a required text statement describing the general focus of the value set including a description of the intended constituent concepts. The Clinical Focus can include information about clinical relevancy, or a statement about the general focus of the value set, such as a description of types of messages, payment options, or geographic locations. The statement should be written as a full sentence with end punctuation (period). Over the course of a value set’s lifecycle, the measure developer should not change the clinical focus in any meaningful way. Format: The purpose of this value set is to [verb] concepts for/of [noun(s)]. Appropriate verbs Identify Represent Describe Define Group Example: The purpose of this value set is to represent concepts for a diagnosis of type I diabetes mellitus.
Data Element Scope	Data Element Scope is a required text statement describing how the data element relates to the value set to which it is bound. This context of use often constrains the semantic type of the allowed constituent concepts. The value set author should write the statement as a full sentence with end punctuation (period). Format: This value set may use a model element in the [Quality Data Model (QDM) or other data model category]. Example: This value set may use a model element in the QDM category of Medication.
Inclusion Criteria	Inclusion Criteria is a required text statement that describes the concept or code criteria the value set author included. The statement should be a full sentence with end punctuation (period). Format: Includes concepts that [verb] [description]. Appropriate verbs Identify Represent Describe Define Group Examples of the form of the description a diagnosis of a procedure for an encounter for/specific to a medication for Example: Includes concepts that describe a medication specific to generic, prescribable esterified estrogen medication. Note: The value set author can provide an optional inclusion criteria statement when a value set has members that are not currently active in the code system (legacy codes) used to build the value set. This optional statement will allow VSAC users to have more information about the use and intent of the value set. This information may help a user determine if the value set would meet their needs or if the inclusion of inactive codes would not be appropriate for their use. Value set authors should include the statement in the inclusion criteria component of the purpose statement of the grouping value set containing the extensional value set with the inactive concepts. The recommendation is to use the statement, "Includes concepts that may no longer be valid in the code system of choice to facilitate lookback periods" to indicate inactive concepts are in the value set. Format: Includes concepts that may no longer be valid in the code system of choice to facilitate lookback periods.
Exclusion Criteria	Exclusion Criteria is an optional text statement describing what specific concept(s) or code criteria the measure developer would normally include, but specifically excluded and why. The statement should include end punctuation (period). It is good practice to populate this field with “No exclusions” if there are no exclusions. Format: Excludes concepts that [verb] [description]. Appropriate verbs Identify Represent Describe Define Group Example: Excludes concepts representing medications used to treat diabetes mellitus but are not commonly associated with severe hypoglycemia.

Value Set Content Best Practices

The standardization of value sets is important, as it improves data comparison across programs, measures, or data sets. Adherence to quality criteria facilitates the reuse of well-defined value sets to advance research studies and promotes the interoperability of health-related systems. Value set authors should clearly understand major principles defining high-quality value sets. These guidelines will help to advance data sharing by helping to standardize and define the content of extensional, intensional, and grouping value sets.

Content	Guidance
Validity	Value set authors should ensure all included concepts correspond to the intent and purpose of the value set. Users of value sets should review and consider subtle nuances of the concepts in clinical or administrative meaning.
Metadata Completeness	Value sets have important metadata to understand the scope of meaning for the included concepts and the intended use, identity, and ownership. It is best practice to include value set name and purpose statement
Non-redundancy	Where possible, each value set should have a clear purpose fitting the desired program use. Multiple value sets with the same scope and use should be avoided particularly if the redundant value sets are used by the same program.
Code List Completeness	A value set should contain all the relevant concepts for a particular data element. Value set authors should ensure the lists are lean and should scrutinize large value sets.
Logical Correctness	A value set should contain only the relevant concepts for a selected data element and the concepts contained in the value set should strictly align with the described purpose.
Concept Property Similarity	Value set member concepts should not vary with respect to their properties and attributes, such as semantic type and term type. For example, a value set intended for prescribable drugs should contain only drugs with the property "Prescribable." This is applicable to concepts that have such properties. The properties should be more similar than dissimilar. For complex cases, value set authors should seek guidance from terminology experts.

Best Practices for Identification of Codes and Code Systems for Value Sets

Topic	Guidance
All Value Set Codes Are Active in the Code System	The value set authors should consider only currently active codes for inclusion into a value set unless they have intentionally included inactive codes in the value set to facilitate a look-back period. This ensures proper maintenance of the value sets.
Descriptors Match Code System Descriptors	Value set authors should make sure any concept descriptions manually added to value sets match the descriptions in the code system to which the concepts belong. The VSAC Authoring Tool provides a descriptor match check as a built-in function. The VSAC Authoring Tool performs this validation during batch import of codes into a value set and during manual insertions of codes and descriptors.
Terminological Correctness	Ensure the value set’s concepts align with the appropriate terminology to represent the data element. When a code system groups concepts into distinct hierarchies, the presence of codes rooted in multiple distinct hierarchies may indicate an incorrect choice of codes. In complex cases, value set authors should consult terminology experts.
Code System Alignment to Standards	Value set authors should base their value set on the code system(s) recommended by the standards depending on the purpose of their value set and the data model (such as the QDM) to which the value set authors may be adhering.

Value Set Harmonization

Value set harmonization is the process of eliminating unnecessary variance between highly similar or duplicative value sets. Duplicative or highly similar value sets are two or more value sets with the same intent as defined by the value set title or purpose statements and containing duplicate concepts. Having highly similar or duplicative value sets can cause confusion and added burden to end users.

Results of value set harmonization may include alterations in one or more of the highly similar value sets to accommodate a new use, e.g., a new measure, or determining the need for separate value sets (including creating a new value set) and explicitly stating the needed differences. This may require the value set author/steward to update the value set metadata. Examples of reasons there may be a need for highly similar, but separate value sets are

different intents for value set use
one value set may include an exclusion of the other value set, e.g., one value set includes gestational diabetes, but gestational diabetes is an exclusion of the other value set

Harmonization Use Cases

There are different value set harmonization use cases.

Value Set Development: When a measure/clinical decision support developer or value set author has a new measure or other need for a value set, they should first look for an existing value set for possible reuse. This is the beginning of harmonization. If an existing value set or values sets is/are close to meeting their needs, they should contact the existing value set steward(s) to discuss making changes to meet the needs of both.

Value Set Updating: When one value set author is updating their value set and finds a highly similar value set, they can reach out to the author/steward of the other value set to see if they can come to a mutual agreement so only one value set is necessary.

Value Set Review for Other Purposes: Occasionally non-value set stewards/authors review value sets, e.g., for research, and identify highly similar value sets. The researchers should review the potentially duplicative value sets, looking for similarities and differences and contact the value set stewards and encourage harmonizing the highly similar value sets or renaming the non-similar value sets.

In each case, the harmonization activity involves the value set stewards/authors of the highly similar value sets communicating and determining if there is a need for separate value sets. If the value set steward is unavailable or indicates they are no longer interested in maintaining the value set, the exploring value set author could ask to take over as steward. If the value set steward is no longer available or does not respond to requests for correspondence, the exploring value set author could contact the NLM Support Center Help Desk explaining they would like to take over responsibility for the value set. Alternatively, the exploring value set author could create a new value set.

Looking for value set similarities and differences

The Value Set Authority Center has a Value Set Comparison Tool to help value set authors compare published extensional, grouping, and intensional expansions of value sets.

Note that value set repositories other than the VSAC exist and may contain value sets and search capabilities for viewing similarities and differences.

Contact ecqi-resource-center@hhs.gov with value set questions or comments.