Handout · Cheat sheet
HL7 v2 Segment Map
Segments, key fields, delimiters & the MSH numbering gotcha
Objective: Read an HL7 v2 message — identify the segments and the fields that matter.
Common segments & their key fields
| Seg | Name | Key fields |
|---|---|---|
| MSH | Message header | 9 type^event · 10 control id · 11 P/T · 12 version |
| EVN | Event type | 1 event · 2 recorded date/time |
| PID | Patient identification | 3 MRN · 5 name · 7 DOB · 8 sex · 11 address |
| PV1 | Patient visit | 2 class (I/O/E) · 3 location · 7 attending |
| ORC | Common order | 1 order control · 12 ordering provider |
| OBR | Observation request | 4 universal service id · 7 observation date |
| OBX | Observation / result | 2 value type · 3 code · 5 value · 6 units · 8 abnormal flag · 11 status |
| AL1 | Allergy | 3 allergen · 4 severity |
| DG1 | Diagnosis | 3 code · 6 type |
Delimiters (declared in MSH-1 / MSH-2)
- | — Field separator (MSH-1)
- ^ — Component separator
- ~ — Repetition separator
- \ — Escape character
- & — Sub-component separator
Message types & the numbering gotcha
- ADT = admit/discharge/transfer · ORM/OMG = orders · ORU = results · SIU = scheduling · DFT = charges · MDM = documents · ACK = acknowledgement.
- MSH-1 IS the field separator '|' and MSH-2 is the encoding characters — so for MSH (only), field n sits at split index n−1. Every other segment: field n = split index n.
Practise this
Practised at HealthAtoms · healthatoms.com — synthetic, educational reference.