US Core Implementation Guide
The US Core Implementation Guide defines a set of FHIR profiles, search parameters, and conformance expectations that establish the minimum data requirements for interoperability in the United States. It is maintained by HL7 and mandated by ONC (Office of the National Coordinator) for certified health IT systems.
Purpose
US Core serves as the foundational IG that other implementation guides build upon. It defines:
- Which FHIR resources must be supported
- Which data elements within those resources are Must Support
- Required search parameters for each resource
- Terminology bindings (which code systems must be used)
USCDI Alignment
US Core is aligned with the United States Core Data for Interoperability (USCDI), a standardized set of health data classes defined by ONC:
| USCDI Data Class | US Core Profile(s) |
|---|---|
| Patient Demographics | US Core Patient |
| Allergies and Intolerances | US Core AllergyIntolerance |
| Problems/Conditions | US Core Condition |
| Medications | US Core MedicationRequest, Medication |
| Lab Results | US Core Observation Lab, DiagnosticReport |
| Vital Signs | US Core Vital Signs (BP, HR, Temp, BMI, etc.) |
| Procedures | US Core Procedure |
| Immunizations | US Core Immunization |
| Clinical Notes | US Core DocumentReference, DiagnosticReport |
| Encounters | US Core Encounter |
| Goals | US Core Goal |
| Care Team | US Core CareTeam |
| Smoking Status | US Core Smoking Status Observation |
Must Support
The Must Support flag in US Core means:
- The sender must include the data element if it is available in their system
- The receiver must be able to process and store the data element (not reject it)
- It does not mean the element is required to be present — it means both sides must handle it
Version History
| Version | Year | USCDI Version | FHIR Version |
|---|---|---|---|
| US Core 3.1.1 | 2020 | USCDI v1 | FHIR R4 |
| US Core 5.0.1 | 2022 | USCDI v2 | FHIR R4 |
| US Core 6.1.0 | 2023 | USCDI v3 | FHIR R4 |
| US Core 7.0.0 | 2024 | USCDI v4 | FHIR R4 |
How Other IGs Build on US Core
US Core is intentionally minimal — it provides the base layer that other IGs extend:
- CARIN Blue Button extends US Core for payer-to-consumer claims data
- Da Vinci PDex extends US Core for payer-to-payer and payer-to-provider exchange
- Da Vinci PAS/CRD reference US Core profiles for clinical data elements
- QI-Core extends US Core for quality measurement and clinical decision support
