X12 837P NM104 Field Guide: Name First Codes and Common Mistakes
NM104 only makes sense once NM102 has told the reader it's looking at a person — populate it for an organization's NM1 loop and you've created a field that has no defined meaning at all.
NM104 is the first-name element of the NM1 segment, populated only when NM102 = 1 (person); it stays blank for organizational NM1 loops like a payer or billing group.
What this element contains
Example
NM104 holds PRIYA, the subscriber's first name, immediately after the last name in NM103. Synthetic claim data.
Where this trips people up
Synthetic or migrated test files sometimes carry a first name in NM104 even when NM102 is set to 2 for an organization, usually because the source system used a single "contact name" field for both people and businesses. Translators that enforce the person/organization distinction will reject the segment; those that don't will pass through data that doesn't match anything a real payer would send.