Migrating from HL7 v2 to FHIR R4: A Practical Engineering Guide

The HL7 v2 Problem

HL7 v2 messages have been the lingua franca of healthcare interoperability since the 1980s. Virtually every hospital information system and lab system in the world can emit an HL7 ADT (Admit-Discharge-Transfer) feed.

The problem is that HL7 v2 is a pipe-delimited, line-based protocol that predates the modern web entirely. Parsing it in 2024 with modern tooling is friction, and connecting it to modern REST APIs requires a translation layer.

The FHIR R4 Alternative

FHIR R4 (Fast Healthcare Interoperability Resources) solves this with a RESTful JSON API where every clinical concept (Patient, Observation, Appointment) is a standardized resource with a consistent URL structure.

GET https://fhir.hospital.org/Patient/12345
GET https://fhir.hospital.org/Patient/12345/Observation

Building the HL7 → FHIR Translation Pipeline

Step 1: Parse the HL7 v2 Feed Use a library like node-hl7-complete or Python's hl7 package to ingest and segment the raw pipe-delimited message.

Step 2: Map to FHIR Resources This is the hardest step. HL7 fields don't map 1-to-1 to FHIR properties. You need a mapping table. For example, the HL7 PID-5 (Patient Name) segment maps to the FHIR Patient.name array.

Step 3: Validate Against the FHIR Profile Use the official FHIR Validator or a library like fhir.js to ensure your constructed resource passes profile validation before writing to the FHIR store.

Step 4: Write to FHIR Server Use a managed FHIR service (like Google Cloud Healthcare API or Azure Health Data Services) or self-host with HAPI FHIR server.

Zero-Downtime Migration Strategy

The key to migrating live clinical systems is a dual-write period. During this phase, every write goes to both the legacy HL7 system and the new FHIR store simultaneously. This allows you to validate parity before cutting over.

Our Data Interoperability service handles end-to-end HL7-to-FHIR migrations for expanding clinic networks.