HL7 v2 (Health Level Seven)
HL7 v2 is the pipe-delimited messaging standard that still powers most hospital interoperability — ADT admissions, ORU results, ORM orders exchanged as segments (MSH, PID, PV1, OBR, OBX) between clinical systems.
Anatomy of a message
An HL7 v2 message is a sequence of -separated segments. Each segment starts with a 3-letter type (MSH header, PID patient identification, PV1 visit, OBR order, OBX observation result), then pipe-delimited fields, caret-delimited components, and ampersand subcomponents. The MSH segment declares the delimiters and the message type (e.g., ADT^A01 for an admission, ORU^R01 for a lab result) plus the version in MSH-12.
The standard is deliberately loose: every site implements it through an implementation guide defining which fields and segments are required for their workflow — which is why HL7 integration is famously parse once, tune per site, and why a structural parser that labels fields is more useful than a rigid schema validator.
v2 vs FHIR
HL7 v2 remains the workhorse inside hospitals — it is embedded in every LIS, HIS, and interface engine — while FHIR is the modern API-facing standard for new development. Most organizations run both: v2 feeds inside, FHIR at the edges. Our articles on message structure and the v2-vs-FHIR comparison go deeper on migration strategy.
Frequently Asked Questions
Is HL7 v2 being replaced by FHIR?
Not any time soon. v2 still runs most intra-hospital messaging (ADT, ORU, ORM) and is embedded in every LIS, HIS, and interface engine. New development targets FHIR, but realistic strategies run both: v2 feeds internally, FHIR APIs at the edges.
What characters does HL7 v2 use as delimiters?
By default: | separates fields, ^ components, & subcomponents, ~ repeats, and \ escapes. The MSH segment declares the actual delimiters a message uses in MSH-1 and MSH-2, and segments are separated by carriage returns.
Related Standards
- •HL7 v2.x messaging standard (versions 2.1–2.9)
- •HL7 FHIR R4/R5 — the modern successor
Free Tools & Resources
Further Reading
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