ONC Standards Bulletin 2026-3

Background

ONC health IT regulations require the use of standard terminologies to exchange health and health-related information. Today, to comply with regulations, implementers must obtain terminology assets from multiple sources, including implementation guides, web sites, and terminology servers. The same asset may appear in multiple locations, sometimes in duplicate or inconsistent versions. As a result, implementers spend significant time locating and verifying the content they need, creating the potential for unnecessary cost, complexity, and inconsistency across the industry.

To address this friction and reduce implementation burdens, ONC has released Cartos, a freely accessible HL7 FHIR terminology service for terminology assets referenced in the ONC Health IT Certification Program (ONC Certification Program). This initial release is available for operational use, with future phases to be informed by user experience and evolving priorities. Cartos allows both application programming interface (API) access to terminology assets and an interactive web browser to explore code systems and value sets, their metadata, contents, and relationships.

The name Cartos is inspired by cartography, the practice of creating maps that make complex landscapes understandable and navigable. We expect Cartos to help the health IT community navigate the complex terrain of clinical terminology.

Cartos FHIR Terminology Service

Cartos simplifies the fragmented terminology discovery and acquisition process by providing a central location for terminology assets and information associated with ONC regulatory requirements. Cartos reconciles scenarios where the same code system or value set is found in more than one location, removing the risk that terminology consumers may use outdated or incorrect content and pass that along to customers.

Cartos also addresses cases in which an implementation guide references terminology that has subsequently been updated, replaced, or moved to a different location. Cartos provides access to the most current terminology content for implementation guides referenced by ONC regulations.

Cartos provides terminology assets in a standard, consistent, and computable format, reducing burden on terminology consumers who must process multiple formats including but not limited to PDF, spreadsheet, and FHIR resources. It also reduces and potentially eliminates terminology divergence in certified products – enabling semantic interoperability and predictable, standards-based exchange nationwide – fostering data quality and artificial intelligence readiness.

Providers can be confident that their health IT developers keep terminology up to date, while patients benefit from their provider being able to accurately record clinical data for analysis, reporting, and communication to other providers.

Cartos complements the Value Set Authority Center (VSAC) by combining the subset of VSAC content required to fulfill terminology requirements for the ONC Certification Program with other sources (e.g., implementation guides) to provide comprehensive collections of terminology assets. VSAC is a major terminology source for Cartos.

What Cartos Includes

Cartos provides access to information about the code systems and value sets referenced by implementation guides incorporated into ONC regulations, as well as implementation guides approved for voluntary adoption through Standards Version Advancement Process (SVAP). The first release supports SVAP 2025 with the SVAP 2026 content to follow later this year.

The way terminology content is made available through Cartos depends on distribution and licensing requirements. While Cartos delivers comprehensive terminology services, it is not a single source for every healthcare terminology:

• For code systems with established distribution mechanisms, such as RxNorm, Cartos provides metadata and a reference to the authoritative source in Unified Medical Language System.
• For proprietary content such as CPT®, Cartos directs users to the authoritative publisher rather than creating an additional licensing or redistribution process. There is more information about how Cartos manages proprietary content in the user documentation on HealthIT.gov.

Accessing and Exploring Cartos

There are multiple ways to access and explore the terminology resources used in Cartos. End-user documentation in the Cartos User Guide directs users to API instructions, explains how to use the web interface, and provides a link to the Swagger page where users can test the API. In addition, there are links to value set collections organized by implementation guide.

The API is publicly accessible and returns the newest available content by default. For those who prefer visual experience, the Cartos terminology browser lets anyone search and navigate connections among regulations, implementation guides, SVAP updates, code systems, and value sets, including terminology that has been updated since an implementation guide was originally published.

How can you help?

We would like your feedback on how we can make this resource more valuable for you. Are we missing any terminology assets you expected to see? Have you experienced any challenges accessing the terminology assets? Are there any features ONC could add that would improve this resource? Your feedback will help further improve the utility of the service and reduce burden on implementers finding terminology assets required in the ONC Certification Program. Please use the Cartos Support Portal to provide input and enter any questions, comments, or suggestions for improvement. For further information on Cartos, please visit the About Cartos webpage.