ADT^A40 — Merge Patient — Patient ID

Merge at Patient ID level with propagation to historical visits. Modernised successor to A18 (Merge Patient Information).

Purpose

A40 merges two Patient IDs. All visits, observations, prescriptions tied to the absorbed ID must be re-attached to the surviving ID. More powerful than A30 (which acts only at Person level).

Segment structure

Structure ADT_A39. MSH, EVN, PID (survivor), MRG (absorbed).

Real-world example

Merge of MR100401 (duplicate) into MR100400 (survivor) for Claire Dubois:

MSH|^~\&|MPI|HOSP01|EHR|CLINIC02|20260518130000||ADT^A40^ADT_A39|MSG00040001|P|2.5.1|||AL|NE
EVN|A40|20260518130000|||MPI004^Manager^Merger^^^MS.|MERGE PATIENT IDS POST-FUSION VISIT IMPACT
PID|1||MR100400^^^HOSP^MR||DUBOIS^CLAIRE^^^MS.||19751120|F
MRG|MR100401^^^HOSP^MR

Acknowledgment (ACK)

MSH|^~\&|EHR|CLINIC02|MPI|HOSP01|20260518130001||ACK^A40^ACK|ACK00040001|P|2.5.1
MSA|AA|MSG00040001

Common errors

• Incomplete propagation: if the receiver does not propagate the merge to historical visits, data is left orphan.
• A40 used in place of A30: A40 has heavy operational cost for the receiver. Reserve for cases with visits.
• No AuditEvent: mandatory.

Related ADT events

See also: ADT^A30, ADT^A18.