FHIR connectors bridge FHIR and non-FHIR systems (legacy EHRs, HL7v2 sources, X12 payer feeds). Four patterns cover most 2026 integration work.
Pattern 1: HL7v2-to-FHIR converter. HL7v2-to-FHIR IG defines mappings. Message ingested, converted, POSTed to FHIR store as Bundle transaction.
Pattern 2: Proprietary EHR API adapter. Legacy EHR proprietary API (Epic, Cerner) translated to FHIR REST. Sidecar service handles auth and format translation.
Pattern 3: X12-to-FHIR converter. X12 837 (claims), 835 (payment) translated to FHIR Claim, ClaimResponse resources.
Pattern 4: Custom format connector. Site-specific formats (legacy CSV, XML, proprietary). Custom code handles ingestion; FHIR REST for output.
Vendor options (mid-2026)
| Connector type | Options |
|---|---|
| HL7v2-to-FHIR | Rhapsody, Mirth Connect, InterSystems, HL7v2-to-FHIR (open) |
| Proprietary EHR API | Vendor-provided, custom builds |
| X12-to-FHIR | Change Healthcare, Availity, custom |
| Custom format | Bespoke |
Build vs. buy considerations
1. Standard formats (HL7v2, X12) → buy commercial or use open source. 2. Proprietary formats → build custom. 3. Volume matters — high-volume warrants custom optimization. 4. Compliance needs matter — vendor certifications.
Common connector failures
1. Incomplete HL7v2 mapping. Edge cases (OBX repeats, ADT^A08) missing. 2. Terminology mapping in code. Should use ConceptMap. 3. No retry semantics. Failed messages lost. 4. Poor observability. Cannot see connector performance. 5. Manual failure handling. Should be automated with dead letter queue.
Operational patterns
1. Retry with exponential backoff. 2. Dead letter queue for repeatedly failing messages. 3. Prometheus metrics on ingest rate, error rate, latency. 4. Alerting on error rate spikes. 5. Regular replay drills.
Investment sizing
1. Buy commercial engine: $100k-$500k initial + ongoing license. 2. Open source engine: 2-4 FTE for setup + ongoing operations. 3. Custom connector: 3-9 months development + ongoing maintenance.
FHIR connectors are integration infrastructure. Choose the right pattern for the format and volume.