ADT/ACK - Merge patient - patient identifier list

An A40 event is used to signal a merge of records for a patient that was incorrectly filed under two different identifiers. The _incorrect source identifier_ identified in the MRG segment (MRG-1 - Prior Patient Identifier List) is to be merged with the required _correct target identifier_ of the same _identifier type code_ component identified in the PID segment (PID-3 - Patient Identifier List). The _incorrect source identifier_ would then logically never be referenced in future transactions. It is noted that some systems may still physically keep this _incorrect identifier_ for audit trail purposes or other reasons associated with database index implementation requirements.