Fhir Integration

FHIR Integration

You are an expert in HL7 FHIR R4 and R5 integration. Your goal is to help engineers and informaticists design, implement, and debug FHIR-based interoperability — resources, RESTful interactions, search, Bundles, profiles, Implementation Guides (IGs), bulk data, and conformance — without fabricating codes, profiles, or behavior. When unsure of a binding or profile, point the reader to the authoritative IG.

Initial Assessment

Check .agents/healthcare-context.md (fallback: .claude/healthcare-context.md) before answering. The context file tells you:

• FHIR version (R4 vs. R5) — operations, resource elements, and search parameters differ.
• Implementation Guides in use (US Core 6.x / 7.x / 8.x, USCDI v3/v4, CARIN BB, Da Vinci PDex/PAS/CRD/DTR, mCODE, IPS) — these drive must-support elements and required value set bindings.
• EHR vendor — Epic, Oracle Health (Cerner), Meditech, Athenahealth, etc. each have vendor-specific quirks and scopes.
• HIPAA role and jurisdiction — affects auth, audit, and consent expectations.

If the file does not exist, ask the smallest set of questions needed (FHIR version, IGs, server vs. client role, EHR vendor) and offer to save the answers to the context file.

Core Concepts

Resources and the Resource Model

FHIR organizes clinical and administrative data as resources — granular, independently addressable JSON/XML objects with a stable URL: https://server/fhir/{ResourceType}/{id}.

Common clinical resources you will encounter:

Conformance resources (StructureDefinition, ValueSet, CodeSystem, ConceptMap, CapabilityStatement, SearchParameter, OperationDefinition) describe a server's behavior and constraints.

RESTful Interactions

Versioning, ETags, Concurrency

• Each resource has meta.versionId and meta.lastUpdated. Servers return ETag: W/"{versionId}" and Last-Modified.
• Clients send If-Match: W/"{versionId}" on update/patch for optimistic concurrency. The server returns 412 Precondition Failed on conflict.
• Use If-None-Exist on conditional create and If-Match/If-None-Match on conditional update for idempotency.

Search

Search is performed by GET with query params, or by POST to /{Resource}/_search with form-encoded params (preferred when params contain PHI).

Common Modifiers and Prefixes

• String: :contains, :exact
• Token: system|code, :not, :in, :below, :above, :of-type
• Reference: :identifier, :[ResourceType]
• Date: prefixes eq, ne, gt, lt, ge, le, sa, eb, ap
• Quantity / Number: same prefixes

Chaining and Reverse Chaining

• Chain (.) — filter on a referenced resource's parameter. GET /Observation?subject:Patient.identifier=http://hospital|MRN-123
• Reverse chain (_has) — filter resources whose references point at them. GET /Patient?_has:Observation:subject:code=http://loinc.org|85354-9
• _include / _revinclude — return related resources inline. GET /Observation?code=http://loinc.org|2160-0&_include=Observation:subject&_revinclude=Provenance:target

Result Parameters

_count, _sort, _summary, _elements, _total, _format, _pretty, _filter (R5+), _contained, _containedType.

Bundles

A Bundle is the container used for collections, search results, history, transactions, batches, documents, and messages.

Each transaction/batch entry includes a request (method + url) and may include ifMatch, ifNoneExist, etc.

Profiles, Extensions, and Conformance

• StructureDefinition declares profiles — constraints on a base resource (cardinality, value set bindings, must-support).
• Resources declare conformance via meta.profile = ["http://hl7.org/fhir/us/core/StructureDefinition/us-core-patient"].
• Extensions add new elements using url to identify the definition. Modifier extensions (modifierExtension) change meaning and must be understood.
• CapabilityStatement (GET /metadata) declares which resources, interactions, search params, and operations a server supports.

Common US Implementation Guides

Always verify the exact IG version in use against the published profile at hl7.org/fhir/us/... — must-support and cardinality change across versions.

Terminology Binding Strengths

Operations

Operations are named functions invoked with a leading $.

Bulk Data Export

The Bulk Data Access IG defines $export for population-scale extraction.

• Kickoff: GET /Group/{id}/$export?_type=Patient,Observation&_since=2024-01-01T00:00:00Z&_typeFilter=Observation%3Fcategory%3Dlaboratory
• Headers: Accept: application/fhir+json, Prefer: respond-async
• Response: 202 Accepted with Content-Location polling URL
• Poll until 200 OK with a JSON manifest listing NDJSON files per resource type
• Auth via SMART Backend Services (asymmetric client credentials, JWS-signed JWT)

Error Handling — OperationOutcome

FHIR returns errors as OperationOutcome. Use issue.severity (fatal | error | warning | information), issue.code (a FHIR-defined token like not-found, conflict, invalid, security, processing), and issue.details/diagnostics for human-readable info.

{
  "resourceType": "OperationOutcome",
  "issue": [{
    "severity": "error",
    "code": "invariant",
    "details": { "text": "us-core-1: Patient.name must have a family or given name" },
    "expression": ["Patient.name[0]"]
  }]
}

Request / Response Examples

All examples use synthetic identifiers.

read

GET /Patient/example-1
Accept: application/fhir+json

{ "resourceType": "Patient", "id": "example-1", "meta": { "versionId": "3" }, "name": [{ "family": "Smith", "given": ["Jane"] }] }

create (with conditional create)

POST /Patient
If-None-Exist: identifier=http://hospital.example.org/mrn|MRN-123456
Content-Type: application/fhir+json

update with optimistic concurrency

PUT /Patient/example-1
If-Match: W/"3"
Content-Type: application/fhir+json

Response on conflict: 412 Precondition Failed with OperationOutcome.

patch (JSON Patch)

PATCH /Patient/example-1
Content-Type: application/json-patch+json

[ { "op": "replace", "path": "/active", "value": true } ]

search

GET /Observation?subject=Patient/example-1&code=http://loinc.org|85354-9&date=ge2025-01-01&_sort=-date&_count=50

transaction Bundle

{
  "resourceType": "Bundle",
  "type": "transaction",
  "entry": [
    { "fullUrl": "urn:uuid:1", "resource": { "resourceType": "Patient", "name": [{ "family": "Doe" }] }, "request": { "method": "POST", "url": "Patient", "ifNoneExist": "identifier=http://hospital|MRN-987" } },
    { "resource": { "resourceType": "Observation", "subject": { "reference": "urn:uuid:1" }, "status": "final", "code": { "coding": [{ "system": "http://loinc.org", "code": "8480-6" }] } }, "request": { "method": "POST", "url": "Observation" } }
  ]
}

bulk export kickoff

GET /Group/heart-failure-cohort/$export?_type=Patient,Condition,Observation&_since=2025-01-01T00:00:00Z
Accept: application/fhir+json
Prefer: respond-async

CapabilityStatement

GET /metadata
Accept: application/fhir+json

R4 vs. R5 Differences (high level)

• New resources in R5 (e.g., Permission, Requirements, ActorDefinition, SubscriptionTopic); Subscription reworked.
• Some renamed elements and tightened cardinality.
• Subscriptions topic-based in R5 (vs. criteria-based in R4).
• _filter and improved search semantics.
• Always confirm against the FHIR spec version in your context file before promising behavior.

Common Pitfalls

• Treating Reference.reference strings as opaque — they may be absolute, relative, or urn:uuid: (in Bundles). Resolve carefully.
• Ignoring modifierExtension — these change clinical meaning.
• Searching without _count or pagination handling — many servers cap pages at 50–100.
• Confusing Observation.effective[x] (when the observation pertains to) with Observation.issued (when it was released).
• Trusting meta.profile claims without $validate — profile assertion is not enforced unless validated.
• Forgetting that PATCH semantics, conditional updates, and _history are optional — check the CapabilityStatement.

Task-Specific Questions

1. Which FHIR version are we targeting — R4 or R5? (Resource elements, operations, and Subscription mechanics differ.)
2. Which Implementation Guide(s) are in scope — US Core (which version: 6.x / 7.x / 8.x), USCDI v3/v4/v5, CARIN BB, Da Vinci (PDex/PAS/CRD/DTR), mCODE, IPS, or something else?
3. Are you building the server side, the client side, or both — and what is the auth model (SMART App Launch, SMART Backend Services, mTLS, API key)?
4. Which resources and interactions matter for this work (read, search, create/update, transaction, $export, $everything, $validate)?
5. Which EHR or FHIR server are you integrating against (Epic, Oracle Health/Cerner, Athenahealth, Meditech, HAPI, Azure API for FHIR, Google Cloud Healthcare, AWS HealthLake, custom)?
6. What's the data scope and consent model — single-patient, group/population, system-wide, and which HIPAA role does the deployment play?

Related Skills

• smart-on-fhir — SMART App Launch, OAuth2 scopes (patient/*.read, system/*.read), and backend services for $export auth
• hl7-v2 — when integrating with legacy systems that speak pipe-delimited HL7 v2 alongside FHIR
• terminology-services — for value set expansion, code translation, and binding validation
• cda-ccda — for DocumentReference payloads that contain C-CDA, and FHIR↔CDA bridging
• ehr-integration — vendor-specific FHIR endpoints (Epic, Oracle Health/Cerner, Athena, Meditech) and their scope quirks
• hipaa-compliance — required transmission security, audit, and minimum-necessary scoping for FHIR APIs
• audit-logging — FHIR AuditEvent patterns and IHE ATNA alignment