HL7 ADT_A37 Unlink Patient Information

A previous patient identity link needs to be removed.
HL7 message structure ADT_A37 groups and segments from HL7 v2.5.1 Hide structure

These are the generated groups and segments for the version selected at the top of the page. The article explains the workflow, and this panel follows the chosen HL7 version.

Message Structure

SegmentNameRequiredRepeatable
MSH
 Message Header Yes No
SFT
 Software Segment No Yes
EVN
 Event Type Yes No
PID
 Patient Identification Yes No
PD1
 Patient Additional Demographic No No
PV1
 Patient Visit No No
DB1
 Disability No Yes
PID
 Patient Identification Yes No
PD1
 Patient Additional Demographic No No
PV1
 Patient Visit No No
DB1
 Disability No Yes

ADT_A37 is the counterpart to link-style identity workflows. It says two patient identifiers should no longer be linked. That usually means an MPI or identity team decided the relationship was wrong or no longer valid.

Unlinking is not the same as unmerging. If clinical data was already merged or moved, A37 by itself may not be enough to reverse that work. It is best understood as removing an association between still-distinct patient identifiers.

A small A37 example

MSH|^~\&|MPI|CITYHOSP|EHR|CITYHOSP|20260715145000||ADT^A37^ADT_A37|ADT370001|P|2.5.1 EVN|A37|20260715144900 PID|1||123456^^^CAMPUS-A^MR||Smith^Jane^Anne^^Ms^^L||19800314|F PV1|1|O|CLINIC1^12^1^CAMPUS-A PID|2||C987654^^^ENTERPRISE^EPI||Smith^Jane^Anne^^Ms^^L||19800314|F PV1|1|O|MPI^LINK^1^ENTERPRISE

What systems do with it

The sender is commonly an MPI or enterprise identity system. Receivers remove the cross-reference relationship between the two PID identities while leaving each patient record intact.

Search services, repositories, portals, and analytics systems may need to remove cached identity links as well as update their primary patient-index table.

How to read the structure

The local ADT_A37 structure looks much like A24: MSH, EVN, and two patient groups with required PID and optional PD1, PV1, and DB1. The two repeated PID groups identify the association being removed.

Implementation traps

Do not try to use A37 as a general rollback for a bad merge. If downstream data was physically moved, the cleanup may require local correction tools, audit review, and system-specific remediation. A37 only tells the receiver to break the patient-information link represented by the identifiers in the message.

Reference notes

The HL7 v2+ ADT_A37 page gives the concise definition: A37 unlinks two patient identifiers.