Healthcare Interoperability
HL7, FHIR, USCDI, and why moving data between systems is still hard.
How we got here
Healthcare interoperability grew up around HL7 version 2, a pipe-and-hat delimited message format still workhorsing hospital integration. HL7 CDA added structured documents. FHIR — REST + JSON + defined Resources — has become the default for new APIs but has not displaced HL7 v2 for high-volume clinical messaging.
Where each standard lives
| Standard | Sweet spot | Typical use |
|---|---|---|
| HL7 v2.x | Point-to-point messaging | ADT, ORU (results), ORM (orders), SIU (scheduling) |
| HL7 CDA | Documents | Discharge summaries, C-CDA for MU |
| HL7 FHIR R4/R5 | APIs | Patient portal, mobile apps, SMART on FHIR, bulk data |
| IHE profiles | Cross-vendor workflow | XDS document sharing, PIX/PDQ identity |
| IEEE 11073 | Device data | Point-of-care monitors, personal health devices |
| DICOM | Imaging | All modalities and PACS |
| NCPDP SCRIPT | Pharmacy | e-Prescribing |
| X12 837/835 | Claims | Billing and remittance |
The state today
Real interoperability projects spend most of their effort on mapping: reconciling how each system encodes the same idea (a medication order, a diagnosis, a device reading) so that meaning survives the transfer.
Common terminologies:
- SNOMED CT — clinical concepts.
- LOINC — labs and observations.
- RxNorm — medications.
- ICD-10 — diagnoses.
- CPT / HCPCS — procedures.
US regulatory push
The 21st Century Cures Act, its information-blocking rules, and the ONC Standards Version Advancement Process now require certified EHRs to expose a FHIR R4 API and to publish the United States Core Data for Interoperability (USCDI) — a common minimum data set that grows on a published cadence.
References & further reading
- 1HL7 FHIR R4 specification (hl7.org/fhir)
- 2ONC — United States Core Data for Interoperability (USCDI)
- 321st Century Cures Act — Information Blocking (45 CFR Part 171)
- 4IHE IT Infrastructure Technical Framework
- 5SNOMED CT International Edition
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