MRG — Merge Patient Information
Appears in ADT A34, A35, A36, A37, A38, A39, A40, A41, A42, A43, A44, A45, A46, A47, A48, A49 messages.
The MRG segment contains the prior identifiers for a patient before a merge or move operation. It is sent in ADT A34 through A40 messages to allow receiving systems to update their patient index when a merge or move occurs.
Real-World Context
MRG messages are among the most dangerous in production environments. An incorrectly executed patient merge can cause clinical data from two different patients to be combined under one record, which is a patient safety event. Always validate the sending and receiving identifiers carefully. When a merge causes problems downstream, the MRG segment is the first place to look.
Field Reference
Click any row to see the full description, common values, and troubleshooting tip.
| # | Field Name | Type | Req | Max Len | |
|---|---|---|---|---|---|
| 1 | Prior Patient Identifier List | CX | R | 250 | ▶ |
| 2 | Prior Alternate Patient ID | CX | O | 20 | ▶ |
| 3 | Prior Patient Account Number | CX | O | 250 | ▶ |
| 4 | Prior Patient ID | CX | O | 20 | ▶ |
| 5 | Prior Visit Number | CX | O | 250 | ▶ |
| 6 | Prior Alternate Visit ID | CX | O | 250 | ▶ |
| 7 | Prior Patient Name | XPN | O | 250 | ▶ |
Example Segment
1MRG||OLDMRN123^^^HOSPITAL^MR|||OLDACCT001^^^HOSPITAL^AN||OLDVISIT001^^^HOSPITAL^VN|DOE^JOHN^A
Related Segments
Used In Message Types
Parse messages with MRG 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 →