X12 275 NM1 Explained: Structure, Fields, and Common Mistakes
A 275 exists to carry supporting documentation for a claim, and NM1 is the segment that answers the most basic question a reviewer will ask about that documentation: whose records are these? Get the identifier wrong here and the attachment lands in the payer's system with no reliable link to a real patient.
NM1 (Individual or Organizational Name) is a reusable X12 segment that, in a 275 attachment transaction, identifies the patient whose medical records are being sent. It carries the entity role this occurrence represents, the patient's last name, and an identification code such as a member ID, giving the receiving system a way to confirm the attachment belongs to the right person before it gets matched to a claim.
The elements that actually matter in practice
Example
A synthetic NM1 identifying the patient (NM101=QC) as Renee Delacroix, with a member ID carried under qualifier MI. Synthetic data only.
Where this trips people up
Because a 275 often travels as a response to a payer's documentation request, teams building test files sometimes populate NM1 with the requesting provider's information instead of the patient's, on the assumption that whoever sent the request already knows who the patient is. The transaction parses without error, but a receiving system that keys attachment matching off the patient's NM103 and NM109 values will fail to associate the records with the correct person, and the attachment effectively goes nowhere.