X12 837I NM101 (Entity Identifier Code): Format, Values, and Testing Notes
A hospital claim can carry four or five NM1 occurrences that look identical except for two characters at the start. Get NM101 wrong and a claim built around a surgery ends up with no operating physician on file at all, or the attending and operating roles swapped.
NM101 is the Entity Identifier Code on an X12 837I institutional claim — a short code that tells the reader which party a given NM1 occurrence names, such as the billing provider, the attending physician, or the operating physician.
Common values on an institutional claim
Example
A synthetic operating physician occurrence: entity code 72 identifies this NM1 as the surgeon on the claim. Synthetic claim data.
Where this trips people up
Because the attending and operating physician loops share the same structure and often appear back to back, hand-assembled or poorly mapped test files sometimes put the same physician's NPI under both entity codes, or transpose the two roles entirely. The claim parses fine either way — nothing about NM1's syntax flags a role mismatch — and the error only becomes visible when a payer's clinical edits expect a surgical procedure code to line up with a distinct operating physician who isn't also listed as attending.