US Core is the HL7 FHIR implementation guide that defines the minimum set of resource profiles, data elements, and interactions a US health IT system must support for nationwide interoperability. It constrains base FHIR — which is deliberately flexible — into concrete, required profiles (Patient, Condition, Observation, MedicationRequest, and more) that align with ONC's USCDI. US Core is what 'FHIR support' actually means in the US regulatory context.
US Core
US Core is the implementation guide that turns FHIR’s flexibility into a floor everyone in US healthcare has to meet. Base FHIR lets a system model almost anything; US Core says these profiles, with these required elements, must be present — which is what makes cross-vendor interoperability actually work.
- Required profiles - Patient, Condition, Observation, MedicationRequest, AllergyIntolerance, and the rest of the clinically essential resources, each with mandatory data elements.
- The FHIR face of USCDI - It is the machine-readable representation of the data classes ONC’s USCDI requires health IT to exchange.
- The real meaning of ‘FHIR support’ - When a US EHR claims a FHIR API, US Core conformance is what makes the claim checkable.
When I score US healthcare, US Core conformance is a sharp separator: a handful of providers (Epic, NextGen, 1upHealth, Aidbox) explicitly assert it, while the large proprietary-REST majority — clearinghouses, scheduling, provider-data, ambient AI — never map to it at all. For an agent trying to read a chart the same way across ten systems, US Core is the only reason that is even possible, and its uneven adoption is exactly why ‘FHIR is mandated’ and ‘FHIR is usable’ remain two different statements.
Referenced in API Evangelist papers
This standard shows up in my published research. These reports read the machine-readable evidence provider by provider — and put this standard in the context of a real sector.
The State of US Healthcare APIs
US Core is asserted by only a few providers (Epic, NextGen, 1upHealth, Aidbox); the proprietary-REST majority never map to it.
Governed by these regulations
A standard is the machine-readable contract; a regulation is the law that requires it. These are the regulations that mandate or drive this standard, catalogued at regulations.apievangelist.com.
ONC Health IT Certification Program
Certified health IT must expose US Core profiles via the standardized FHIR API.
21st Century Cures Act
The information-blocking rule effectively mandates US Core as the floor for API access.
