← ReferenceStandards
What is HL7 v2?
HL7 version 2 (HL7 v2.x) is a pipe-delimited message standard created in 1987. Despite being 35+ years old, it is still the most widely deployed health IT standard in the world — the backbone of hospital ADT feeds, lab results, and order messages in the vast majority of existing healthcare systems.
ADT^A01 — Admit Patient (HL7 v2 message)
MSH|^~\&|HIS|FNSP|LAB|FNSP|20240315120000||ADT^A01|MSG001|P|2.5 EVN|A01|20240315120000 PID|1||987654321^^^2.16.840.1.113883.2.9.4.3.2^ISO||Horváth^Jana||19850315|F|||Mlynská 12^^Bratislava^^81105^SK
Message structure
| Concept | Description |
|---|---|
| MSH | Message header — encoding, sender, receiver, timestamp, message type |
| PID | Patient identification — name, DOB, gender, address, identifiers |
| EVN | Event type — the trigger (A01 = admit, A08 = update, A18 = merge) |
| OBX | Observation — a single result, used in lab messages (ORU^R01) |
| ORC/OBR | Order and order detail — used in ORM (order) messages |
HL7 v2 vs FHIR
- Format: pipe-delimited text vs JSON/XML
- Transport: MLLP (raw TCP) vs HTTP/REST
- Query: no standard REST — messages are push-only
- Status: dominant in internal hospital systems, being replaced at integration boundaries by FHIR