^A34
ADT^A34 — Merge Patient Information - Patient ID Only
Sent to merge duplicate patient identifiers while retaining the demographics from the surviving record. The prior patient's identifier (in MRG.1) is merged into the surviving patient (in PID.3). Only patient identifiers are merged — visit records remain associated with the surviving patient.
When Is This Sent?
When a duplicate MRN or patient identifier is discovered and the duplicate ID must be retired and consolidated under the correct patient record. The surviving record in PID already contains the correct demographics.
Real-World Usage
A34 was the original patient-ID merge event before A40 was introduced. Many older systems still use A34. It is functionally similar to A40 but operates specifically on patient identifier lists. A34 ensures that any future lookup on the old (prior) MRN redirects to the surviving patient. If downstream systems still receive A34 from legacy sources, ensure they resolve the old identifier to the surviving record.
Message Structure
Segment names link to their field-level reference pages.
Example Message
Realistic example with fake patient data. Paste into the HL7 Message Viewer to explore interactively.
1MSH||^~\&|EPIC|HOSPITAL_A|MIRTH_PROD|PACS|20260312110000||ADT^A34^ADT_A34|MSG00105|P|2.5.1 2EVN||A34|20260312110000 3PID||1||123456^^^HOSP_A^MR||Smith^John^M^^Mr.||19850315|M 4MRG||888888^^^HOSP_A^MR
Troubleshooting Scenarios
Studies associated with old MRN still not visible under surviving patient
Cause
PACS received A34 but only retired the identifier without relinking historical studies from the old MRN to the surviving patient.
Fix
Confirm with the PACS vendor that A34 triggers full study relinking, not just identifier retirement. Some PACS systems require a separate manual merge operation or a supplementary message to relink historical studies.
Common Confusions
ADT^A34 (Merge Patient ID Only) vs ADT^A40 (Merge Patient Identifier List). A34 is the older, more limited merge event. A40 is the modern standard and should be used in new implementations. For most downstream systems, A34 and A40 can be handled identically — both use PID (surviving) and MRG (prior). Prefer A40 for new interfaces.
Related Message Types
Segment Reference
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