A Claim Adjustment Reason Code (CARC) states why a claim line was adjusted or denied — for example, CO-50 (not medically necessary) or CO-97 (bundled). A Remittance Advice Remark Code (RARC) adds supplemental detail. Some CARCs, like CO-16, require at least one RARC to be actionable, because the CARC alone is too generic.
The difference
- CARC — the adjustment reason (the 'why'), with a group code (CO, PR, OA, PI) that says who's responsible.
- RARC — a remark that supplements the CARC with specifics (e.g., exactly which information is missing).
- Generic CARCs (like CO-16) must be paired with a RARC to tell you what to fix.
Frequently asked
Which do I act on first?
The CARC tells you the reason and who's responsible; the RARC tells you the specifics. For a generic CARC like CO-16, the RARC is what actually drives the fix.
Where do I see them?
On the EOB and on the ERA (835) — both carry the same CARC/RARC codes for a claim.
Primary sources: X12 — Claim Adjustment Reason Codes (CARC); X12 — Remittance Advice Remark Codes (RARC). General information, not legal or medical advice — confirm against the governing rule for the plan type.
Related guides
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