Every denial code, decoded

Contractual Obligation (CO)

The provider's contract bars billing you - usually you should not owe this.

• CO-109 - You sent the claim to the wrong insurer (or wrong plan). This payer isn't responsible for it.
• CO-119 - You've hit a limit your plan sets on this benefit (e.g., a cap on visits or dollars for the year).
• CO-151 - The insurer thinks you received this service too often, so it won't pay for the extra.
• CO-16 - Your claim was denied because something was missing or entered wrong - not because the care isn't covered. It's an administrative/paperwork problem.
• CO-167 - The insurer won't pay because the diagnosis on the claim isn't one it covers for this service.
• CO-18 - The insurer thinks this exact claim was already submitted, so it rejected the second one as a duplicate.
• CO-197 - The care needed prior authorization (advance approval) and the insurer didn't have it on file, so it denied the claim.
• CO-204 - The item simply isn't a covered benefit under your specific plan.
• CO-22 - The insurer thinks another insurance plan should pay first (or instead). It's a coordination-of-benefits issue.
• CO-252 - The insurer needs extra paperwork (like medical records or notes) before it can decide on the claim.
• CO-29 - The claim was submitted too late, after the insurer's filing deadline.
• CO-45 - This isn't really a denial - it's the normal discount between the provider's full charge and the contracted rate. The provider writes off the difference.
• CO-50 - The insurer decided this care wasn't medically necessary, so it won't pay. This second-guesses your doctor's judgment.
• CO-96 - The insurer says this service isn't covered by the plan. The paired remark code should say the specific reason.
• CO-97 - The insurer says this service is already paid for as part of another procedure, so it won't pay separately (it was 'bundled').

Patient Responsibility (PR)

An amount the plan says you may owe (deductible, copay, coinsurance, or a non-covered charge).

• PR-1 - Not a denial - this is the part of the bill applied to your annual deductible, which you owe before insurance starts paying.
• PR-2 - Not a denial - this is your coinsurance, the percentage of the cost you share after meeting your deductible.
• PR-204 - Same as CO-204, but the insurer says YOU are responsible for the cost because it's non-covered.
• PR-3 - Not a denial - this is your fixed copay for the visit or service.

Remark Codes (RARC)

Remark codes that pair with a denial to explain the specific reason.

• MA130 - A remark code meaning the claim had bad/missing info. Importantly, you can't appeal it as-is - it must be corrected and resubmitted first.
• N479 - A remark code (pairs with a denial like CO-16): the insurer needs the EOB from your primary plan before it will pay.

Insurer-specific appeal guides

• Aetna - Medical necessity
• UnitedHealthcare - Out-of-network
• Cigna - Prior authorization