US Core

US Core is the minimum FHIR profile set ONC requires US-certified EHRs to expose. It's the baseline every healthcare app targeting US providers should design against — Epic, Cerner/Oracle, athenahealth, Meditech all publish US Core-conformant endpoints.

What it covers

US Core defines profiles (constraints + required fields + value set bindings) for the resources that map onto the USCDI (United States Core Data for Interoperability):

• Patient demographics + identifiers
• AllergyIntolerance, CarePlan, Condition, Encounter, Goal, Immunization, Procedure
• DocumentReference (clinical notes)
• Coverage (insurance)
• Lab Observations + Vital Signs (two distinct profiles on Observation)
• MedicationRequest + Medication
• Organization, Practitioner, PractitionerRole, Location

Each release ratchets up required fields + must-support markers — what's optional in US Core 3.1.1 is required in US Core 6+.

Versions and ONC certification

| Version | FHIR base | ONC tied to | |---------|-----------|-------------| | 3.1.1 | R4 | HTI-1 (legacy) | | 6.1.0 | R4 | HTI-1 transition | | 7.0.0 | R4 | HTI-2 (2025+) |

If you're building against a US-certified EHR mid-2026, target US Core 6.1+ unless your stakeholder says otherwise.

Where it bites

• Search params: US Core requires specific search params to be supported (patient, category, date ranges, etc.). Don't assume search support beyond what US Core mandates.
• Must-support ≠ required: an EHR can omit a must-support field for a specific patient if they don't have data, but they cannot reject your read for asking for it.
• Vital Signs vs. Lab profile is a common trip-wire — they're different Observation profiles with different code bindings.

The connection to everything else

Almost every US-targeted IG (DaVinci, SDOH-CC, mCODE, SMART App Launch) profiles on top of US Core. Build to US Core first, then layer on the IG-specific profiles.