Value Set Information

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

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

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

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.

Value Set Review and Maintenance

Value set users expect a value set’s author and/or steward to review and update their value set as terminology, clinical standards, evidence or guidelines, and program needs change over time. The appropriate application of VSAC review and maintenance statuses will increase transparency to the value set’s review and maintenance activities. Table 1 provides value set review and maintenance components and considerations.

Table 1. Value Set Review and Maintenance Components and Considerations
Maintenance	Guidance & Considerations
Frequency of Review	At a minimum, value set authors and stewards should review their value set(s) contents annually and base the review on program or use requirements. Contents may include specific value set codes, value set purpose, or review and maintenance status. For example, authors and stewards should review new codes or legacy codes that may be appropriate to add, depending on the terminology, and review inactive codes for removal or retention.
Review and Maintenance Status	A review and maintenance status for a value set is available in VSAC in both the authoring and public search tabs. In the public Search Value Sets tab, find the review and maintenance status in section C. Value Set Expansions. For each value set, the Value Set Details tab has a Metadata tab providing Expansion Details with more information on the expansion profile and the review and maintenance status descriptions. In the Authoring tab, find the review and maintenance status under the column titled Review Status. For each value set, the Review/Maintenance tab provides the ability to update the review and maintenance status. All value set review and maintenance statuses begin with the publication of the value set. A published value set will have one of five review and maintenance statuses: Active Not Maintained Deprecated Retired Experimental See Table 2 for more information on review and maintenance statuses.
Use	In VSAC, a value set author and steward can track the number of value set downloads to approximate use of the value set. An increase in downloads of a value set may be an indication of a value set’s use (see Value Set Usage Summary for Authors and Stewards for additional details). The usage summary provides the number of downloads of the value set. Value set authors and stewards can apply the usage summary to approximate the use of the value set. The usage summary can assist the stewards and authors to make decisions regarding continued maintenance and assigning a particular maintenance status.
Transfer of Stewardship	If a steward no longer wants to maintain a value set that is used, stewards can transfer ownership of a value set directly to another steward in VSAC. All value sets in VSAC have a Contact Steward icon for Unified Medical Language System (UMLS) licensed users to contact the value set steward on record to request transfer of stewardship of the value set. Both parties must agree to the transfer of the stewardship for a value set. After agreement, the stewardship can be changed using the VSAC Change Value Set Ownership function. If the steward is not available to transfer stewardship through VSAC, the National Library of Medicine (NLM) can make the transfer. The user requesting stewardship transfer can send an email to nlm-support@nlm.nih.gov

A. Value Set Review and Maintenance Statuses Guidance

The value set author and steward uses the review and maintenance status of a value set to

• inform value set users the value set is being maintained
• help users make decisions on potential use or reuse of a value set
• provide transparency of the review and maintenance activities

The review and maintenance status also shows measure implementers and users the value set is likely to contain up-to-date content appropriate for a certain use when it has an active status.

As the author and steward updates the value set, certain guidance applies to the status: 

• The value set review and maintenance status applies to a single, specific value set definition version, and not “all versions” of a value set.
• The value set review and maintenance status does not apply to the use of a value set in a specific program.
• Value Set Review Status and Maintenance History tracks the last date on which the author or steward reviewed the value set metadata, definition, or expansion.

The value set review and maintenance statuses are Active, Experimental, Not Maintained, Deprecated, and Retired. The VSAC does not currently have business rules on timings to transition a value set from Not Maintained to Deprecated, or from Deprecated to Retired. However, there is automatic transition timing from Active to Not Maintained.

The VSAC Support Center provides definitions for each value set review and maintenance status. For additional information and considerations on each review and maintenance status, refer to the guidance in Table 2.

Table 2: Value Set Review and Maintenance Status Guidance
Review and Maintenance Status	Guidance and Considerations
Active	The Active status indicates a value set underwent review and maintenance, if deemed necessary by the steward or author. The value set will remain as Active in VSAC if a value set author or steward either Publishes a new definition version of a value set Selects the “Mark as Reviewed” button, which restarts the value set review and maintenance cycle timeline. Value set authors and stewards can check “Mark as Reviewed” anytime. This option is always available for value set authors and stewards to indicate they have reviewed a value set. To keep a value set in Active status, the author and/or steward should review their value set at least every 12 months. Reviews should be based on the value set’s code system updates, content alignment with intent, potential clinical evidence changes, and end user feedback. If the value set author or steward has not marked the value set as reviewed or re-published after 12 months, NLM will send monthly email notifications for a total of 5 months thereafter. Hence, re-publishing or marking a value set as reviewed will keep the status active for a total of 17 months. Value sets used in CMS or other federal health programs or currently utilized in systems should have an Active status. Even in the event a value set uses a code system the owner (e.g., National Center for Health Statistics) is no longer updating (e.g., ICD-9-CM), the value set author and/or steward should still review the value set for continued use and mark as reviewed if the value set is still applicable for its intended purpose.
Not Maintained	An author or steward should mark a value set as Not Maintained if they do not plan to review, update, re-publish, use, or otherwise follow any maintenance process for their value set. In addition, an automated process can assign this status when the author or steward does not complete actions to keep the value set in an active status and there is no record of review or maintenance for 17 months. VSAC will send value set review and maintenance notifications when a value set author or steward does not perform any review or maintenance within the past year. Based on timing of review and update cycles, in some situations, the steward or author may include a Not Maintained version in a current program release if a value set author or steward fails to complete an annual review and maintain an Active value set status. If a value set goes to a Not Maintained status, neither NLM nor the value set author or steward can change the value set’s review status back to Active. The value set author or steward must create and publish a new definition version to update the value set status. If creating a new version of a Not Maintained value set, the value set author or steward should use best practices in value set creation, review, and maintenance, which includes reviewing the value set’s contents and purpose. Expansions cannot be created for value set definitions with this status (see Section C for more information on expansions).
Deprecated	Value sets users should not use a value set with a Deprecated status for any use. When a value set is set to Deprecated status, all previous versions of the value set will also be set to Deprecated. A deprecated value set’s contents are no longer relevant and value set users should not use the value set. For example, there may have been updates to a clinical guideline changing the clinical purpose and content drastically, a value set author or steward may select to deprecate the value set. The value set author or steward cannot change the Deprecated status to Not Maintained or Active. The value set author and/or steward must create and publish a new definition version and review and update the content accordingly. Expansions cannot be created for value set definitions with this status.
Retired	Value sets users should not use a value set with a Retired status for any use. When a value set is set to Retired status, all previous versions of the value set will also be set to Retired. A retired value set may include relevant content but may be set to Retired by an author or steward because they have chosen to no longer maintain the value set. For example, they may no longer use the value set and are not aware of any other continued use of it. The value set author or steward cannot change the Retired status to Not Maintained or Active. The value set author and/or steward must create and publish a new definition version. If a value set author or steward determines they will no longer maintain a value set, they may opt to change the value set to the Retired status. Expansions cannot be created for value set definitions with this status.
Experimental	Value sets in Experimental status follow the same review timeline as Active value sets. Value set users should not use a value set in Experimental status except in the context of piloted use. Value set authors and stewards cannot change the status of a published definition version with the Experimental status.

B. Grouping and Member Review and Maintenance

A grouping value set may contain a value set with a status of Not Maintained and continue to have the Active status. Currently, there is no warning or functionality to notify a value set author or steward that a grouping value set they own now has a Not Maintained value set as a member or keep them from adding a Not Maintained value set to a grouping value set.

It is up to the value set author and/or steward to ensure a grouping value set contains the correct content. It is possible an Active grouping value set contains one or more value set(s) with a Not Maintained status. A user, such as the grouping value set’s steward, may use the Contact Steward button to reach the steward of the Not Maintained extensional value set(s) for more information. If the steward indicates they will not review and maintain the value set(s), upon request, the value set steward may transfer stewardship (see Table 1). After completion of transfer of stewardship, the new value set steward should review the value set, following best practices, and create and publish a new definition.

C. Value Set Expansions

A value set expansion is the set of concept codes (the member set) end users download and implement in systems. An expansion member set is the result of using specified version(s) of a code system, applied to a specified value set definition. The NLM generates the expansion using the most currently available code system and value set version. NLM marks this expansion as "Latest."

In the VSAC, a download of a value set expansion version will include the member set expansion list with the codes, code descriptions, the code system name, identifier, and the code system version used for each member in the expansion set. Note, in VSAC, the NLM uses the status of the value set definition to create the "expansion status" of the expansion. This is true when the expansion was created in the past, the expansion status will change to align with the status of the definition at the time of viewing or download.

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

 

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

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 intentional expansions of value sets.