Remark code lookup

A claim adjustment reason code (CARC) says why the payer paid something other than what was billed: CO-16, PR-204, CO-45. A remittance advice remark code (RARC) adds the detail — which field was missing, which document they want, which policy they applied — or carries information that is not a denial at all. The reason code decides the money; the remark code tells you what to do about it.

They are claim adjustment group codes, and they say who is liable for the amount. CO, contractual obligation, means the provider absorbs it and may not bill the patient. PR, patient responsibility, means the patient owes it. OA, other adjustment, assigns it to neither. PI, payer initiated reductions, is a reduction the payer made on its own account, usually appealable. The same reason number can appear under different groups, and the group changes what you do next.

Because X12’s usage note for reason code 16 requires the payer to send at least one remark code with it. On its own, 16 says only that the claim lacks information or has a billing error; the remark code — M51 for the procedure code, N382 for the patient identifier, MA130 for an unprocessable claim — says what. If a payer sends 16 with no remark, ask them for it before working the claim.

Yes. Reason code 204, "not covered under the patient’s current benefit plan", is PR-204 when the payer holds the patient responsible and CO-204 when a contract stops the provider billing the patient for it. Same reason, different debtor. Verify eligibility on the date of service before a PR amount reaches a statement; if coverage was active, dispute the group code rather than bill the patient.

That the code is informational. X12 marks remark codes that explain something about the remittance, rather than about a denial or adjustment, with the word Alert. N381, for instance, tells you to consult the contract; it does not deny anything. The liability on that line is decided by the reason code beside it.

X12 publishes a stop date when it retires a code, and the decoder shows it. A payer still sending a deactivated code is on an old code set, or printing its own explanation-of-benefits codes in the remark position. Ask the payer which current code they mean; do not work the claim on the strength of a retired description.

The reason and remark code descriptions are the X12 external code lists, reproduced verbatim, retrieved 2026-09-10. X12 updates the lists three times a year. Everything after the official text — the plain reading, the “read together” sentences and the next move — is our working guidance, written from working these codes, and is labelled as ours.