HL7 v2
HL7 Version 2.x
HL7 v2 is the pipe-and-hat messaging standard that still carries most real-time clinical data between hospital systems — admissions, orders, results, and more.
HL7 v2 (versions 2.1 through 2.9) is the workhorse messaging standard for real-time clinical data exchange inside hospitals and between hospitals and their trading partners. It encodes events as delimited text messages built from segments (MSH, PID, PV1, OBX, DG1, and so on) separated by pipes (|) and other delimiters — the reason it is often called the "pipe-and-hat" format.
Common message types include ADT (admit/discharge/transfer), ORM/OMG (orders), ORU (observation results, e.g. lab and radiology), SIU (scheduling), MDM (documents), DFT (billing), and VXU (immunizations). Because HL7 v2 predates the modern web, it is optimized for high-throughput, event-driven messaging rather than for RESTful APIs.
HL7 v2 is not disappearing. Most health systems still run large v2 estates for their core operational flows, even as regulation pushes them to also expose FHIR APIs. That coexistence — "must expose FHIR, still run v2" — is the structural gap that bidirectional translation fills.
How this relates to Health1st
Health1st's Transformation Agent parses and serializes HL7 v2 messages segment by segment, and its Mapping Agent proposes the field-level mappings from v2 into FHIR (and back). A sample ADT^A01 admission maps PID → Patient, PV1 → Encounter, and a DG1 diagnosis like ICD-10 E11.9 → a FHIR Condition, validated against US Core — with a human reviewing every mapping.
Related terms
FHIR is HL7's modern, web-native standard for exchanging healthcare data as modular JSON/XML resources over RESTful APIs.
ADT is the family of HL7 v2 messages that communicate patient admissions, discharges, transfers, and demographic updates — the most common real-time feed in a hospital.
C-CDA is the HL7 XML standard for clinical documents such as the Continuity of Care Document, discharge summary, and referral note.
US Core is the HL7 implementation guide that constrains FHIR resources into the specific profiles US regulation requires, binding them to USCDI data elements.
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