Health Language Blog

The Difference Between Intensional and Extensional Value Sets

Posted on 06/03/15


Value sets, also referred to as code groups, help healthcare providers and payers define clinical concepts.

Each value set is essentially a bag of codes that can represent a particular disease or a type of medicine. A value set consists of terms and their associated numerical codes, which are taken from standard terminologies such as ICD-10, SNOMED CT®, RxNorm and LOINC®.  Value sets have a number of use cases. Those include creating Clinical Quality Measures (CQMs), defining a patient population cohort, defining decision support rules, and developing application pick lists.

A value set may be structured as intensional or extensional. The terms intensional and extensional come from the fields of mathematical logic and set theory. In the healthcare context, the distinctions between an intensional and an extensional value set have important implications for code group management.

The Terms Defined

An intensional value set is typically algorithmically defined. That is, the code group is defined as a rule. The rule might say, for example, extract all codes with the word diabetes. The key benefit of intensional code groups is that they can be dynamically updated. Dynamic updating helps healthcare organizations keep current when new drugs (and their associated codes) become available or codes for diseases and other clinical concepts change. An intensional value set designed to contain all of the drugs in the beta blocker category can automatically receive a new beta blocker’s code as soon as it hits the market.

Extensional value sets, meanwhile, are enumerated lists of codes that are not algorithmically based. According to HL7 International, “value sets defined by extension are comprised of an explicitly enumerated set of codes.” Integrating the Healthcare Enterprise, in its Sharing Value Sets white paper, states that extensional value sets are “defined in terms of a list of concepts.

One possible application for extensional value sets is in creating CQMs, which play a pivotal role in the federal government’s Meaningful Use initiative. In order to qualify for the program's financial incentives, physicians and hospitals must submit CQM data from a certified electronic health record (EHR) system.

But while an intensional value set may be dynamically updated, the same isn’t true for its extensional counterpart. As a consequence, an extensional value set tends to become stale rather quickly.

Controlling The Definitions

Health Language offers a code group management tool that lets healthcare organizations control the definition of value sets or code groups, whether intensional or extensional. In the case of an intensional value set, they can also determine how the code groups are updated. In some circumstances, an organization may not want to have code groups automatically updated without having an opportunity to opt in to the update. A clinical researcher, for instance, conducting a historical analysis across a patient population will need to closely control the variables and won’t want a code group’s definition suddenly changing in the course of the study. For those circumstances, the Health Language tool provides the ability to postpone a suggested update by locking in the version of the underlying code groups.

On the other hand, a healthcare system running a care management program may want to identify all its patients with diabetes. In this situation, the user may forgo the opt-in feature and allow a value set to be automatically updated. This option pulls in the latest codes involving diabetes diagnoses, so clinical informaticists can identify all the patients who belong in the population.

Clinical Building Blocks

Healthcare organizations will likely find themselves needing to work with value sets more and more in the coming years. Indeed, code groups are becoming the clinical building blocks of important healthcare programs and initiatives. Code groups, as noted, help healthcare organizations satisfy reporting requirements like the Meaningful Use and HEDIS programs. In addition, code groups can help care management programs create cohort identification rules to properly identify at-risk patients.

Understanding the difference between an intensional and an extensional value set can help you make better decisions when defining your code groups. What are your top code group management challenges? Leave your comments below.

enterprise terminology management


Topics: value sets

About the Author

Brian Diaz is the Director of Integrated Solutions with Health Language, part of Wolters Kluwer Health. When not working, Brian is soaking up the Colorado experience with his family but still cheers on the Golden Gophers.