A merge has been done at the visit identifier level. That is, two PV1-19-visit number identifiers have been merged into one.
An A42 event is used to signal a merge of records, for a visit that was incorrectly filed under two different visit numbers. The "incorrect source visit number" identified in the MRG segment (MRG-5-prior visit number) is to be merged with the required "correct target visit number" identified in the PV1 segment (PV1-19-visit number). The "incorrect source visit number" 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.
An A42 (merge visit - visit number) event is intended for merging visit records without merging other identifiers. Any other identifiers that were previously associated with the "incorrect source visit number" are now associated with the "correct target visit number."
Each superior identifier associated with this visit identifier level should have the same value in the PID and MRG segments, or the MRG and PV1 segments, as appropriate.
See Section 3.5.2, "Merging patient/person information," for a discussion of issues related to the implementation of merge messages.
All data associated with the "correct target visit number" are treated as updated information.
ADT ADT Message Chapter
MSH Message Header 2
EVN Event Type 3
{ PID Patient Identification 3
[ PD1] Additional Demographics 3
MRG Merge Information 3
[ PV1] Patient Visit 3
}
ACK General Acknowledgment Chapter
MSH Message Header 2
MSA Message Acknowledgment 2
[ ERR ] Error 2