FHIR defines 140+ resources but production EHR integrations touch a smaller set. Understanding which resources are the workhorse and which are edge-case avoids overinvesting in exotic resource support.
Tier 1: Core clinical (must-have for any US integration)
- Patient — identity, demographics - Encounter — visits and admissions - Observation — labs, vitals, notes - Condition — diagnoses - MedicationRequest — prescriptions - Practitioner — clinicians
All six are US Core-profiled; every EHR integration handles them.
Tier 2: Common secondary
- Procedure, Immunization, AllergyIntolerance, DocumentReference, DiagnosticReport, ServiceRequest, MedicationAdministration, MedicationDispense
Covered by US Core, expected for most clinical use cases.
Tier 3: Payer / regulatory
- Coverage, ExplanationOfBenefit, Claim, ClaimResponse — CMS-0057 Payer Access - Consent — patient authorization tracking - Task — workflow items
Tier 4: Specialized
- QuestionnaireResponse — SDC form outputs - MeasureReport — quality reporting - CarePlan — care coordination - Communication — messaging
Rarely-touched
Research resources (ResearchStudy, ResearchSubject), device tracking resources at the granular level, some administrative resources.
Coverage requirement per use case (mid-2026)
| Use case | Tier coverage needed |
|---|---|
| Basic EHR data exchange | Tier 1 |
| Full US Core conformance | Tier 1 + 2 |
| CMS-0057 Payer Access | Tier 1 + 3 |
| SDC forms integration | Tier 1 + QuestionnaireResponse |
| Quality reporting | Tier 1 + MeasureReport + CQL |
| Full US Core + Da Vinci | Tier 1 + 2 + 3 |
Most EHR integrations succeed by covering Tier 1 and 2 well, then adding specialized resources as use cases demand. Trying to support all 140+ resources up-front burns budget for no operational benefit.