MSA — Message Acknowledgment
Appears in ACK messages and application-level acknowledgment responses. Always paired with an MSH segment.
The MSA segment is returned by the receiving system to confirm receipt of a message. It carries the acknowledgment code and echoes back the original message control ID so the sender can match the ACK to the original message.
Real-World Context
MSA is how you know whether a message was accepted or rejected. The acknowledgment code in MSA.1 is critical for error handling — AA means accepted, AE means application error, AR means rejected. Monitoring for AE or AR codes in production is essential for catching silent failures before they impact patient care.
Field Reference
Click any row to see the full description, common values, and troubleshooting tip.
| # | Field Name | Type | Req | Max Len | |
|---|---|---|---|---|---|
| 1 | Acknowledgment Code | ID | R | 2 | ▶ |
| 2 | Message Control ID | ST | R | 199 | ▶ |
| 3 | Text Message | ST | O | 80 | ▶ |
| 4 | Expected Sequence Number | NM | O | 15 | ▶ |
| 5 | Delayed Acknowledgment Type | ID | O | 1 | ▶ |
| 6 | Error Condition | CE | O | 250 | ▶ |
Example Segment
1MSA||AA|MSG00001|Message accepted successfully
Related Segments
Used In Message Types
Parse messages with MSA in real time
Paste any HL7 message into our free viewer. Decodes every segment and field instantly, client-side.
Open HL7 Message Viewer →Need HL7 mapping templates?
The HL7 Integration Toolkit includes field mapping worksheets, interface spec templates, and a go-live checklist for every major HL7 message type.
View HL7 Integration Toolkit →