X12 270/271 N3 Segment Guide: Fields, Format, and Testing Gotchas
N3 shows up wherever a 271 response needs to give a mailing address — the subscriber loop, the provider loop, sometimes both — and it only ever carries the street portion. City, state, and ZIP live one segment later in N4, which means an N3 by itself is only half a usable address.
N3 (Party Location) is the segment in an X12 271 eligibility response that carries the street address for whichever party the surrounding loop describes — a subscriber, a dependent, or a provider. It holds up to two free-form address lines and always pairs with an N4 segment for city, state, and ZIP.
The elements that actually matter in practice
Example
N301 carries the street number and name, N302 carries the suite detail on a separate line. Synthetic 271 response data.
Where this trips people up
Because N302 is optional, test fixtures tend to build every N3 with a single populated line and never exercise the two-line case. Real payer data routinely splits a street address across both elements — building number and street on N301, suite or unit on N302 — and a parser that only reads N301 will silently drop the unit number for every multi-tenant address it processes, which is exactly the kind of address that needs it most.