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Denial Code Lookup

Every Claim Adjustment Reason Code (CARC) and Remittance Advice Remark Code (RARC) from the official X12 lists, explained in plain English: what it means, common causes, how to fix it, and whether it is still active.

407 reason codes (110 deactivated) · 1216 remark codes (79 deactivated) · X12 lists retrieved September 25, 2026

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How to read a denial code

A code like CO-16 has two parts. The letters are the group code, which says who is responsible for the adjusted amount. The number is the reason code (CARC), which says why the claim or line was adjusted. A remark code (RARC), such as N290, often follows to give the specific detail.

CO Contractual Obligation
The provider is responsible for the adjusted amount under a contract or regulation. It is written off and generally cannot be billed to the patient.
PR Patient Responsibility
The patient may owe the amount, such as a deductible, coinsurance, or co-payment. It can be billed to the patient according to the plan and your agreements.
OA Other Adjustment
Used when neither CO nor PR applies, for example amounts already considered by a prior payer in coordination of benefits.
PI Payer Initiated Reduction
The payer reduced the amount for a reason it considers outside the patient's responsibility, where no contract applies. Whether the patient can be billed depends on the situation and the payer.
CR Correction and Reversal
Corrections and reversals of prior claims. It is not part of the current (5010) version of the 835, so it appears only on older remittances.

For a deeper walkthrough, read how to use CARC and RARC codes to analyze denials.

Denial code FAQ

What is a denial code?

A denial code is the Claim Adjustment Reason Code (CARC) a payer puts on an electronic remittance advice (ERA, or 835) or explanation of benefits to explain why a claim or service line was paid differently than billed. It is combined with a group code such as CO or PR, which is why codes appear as CO-45 or PR-1.

What is the difference between a CARC and a RARC?

A CARC gives the reason for the adjustment. A Remittance Advice Remark Code (RARC), such as N290 or MA130, adds detail about that reason, like which claim field was missing. Many CARCs require at least one RARC.

What do CO, PR, OA, and PI mean in front of a code?

They are group codes that say who is financially responsible for the adjusted amount. CO means a contractual obligation the provider writes off, PR means patient responsibility, OA means other adjustment, and PI means a payer-initiated reduction.

What happens to a code that X12 deactivates?

Payers should stop using it on new remittances after the deactivation date, but it can still appear on older ERAs, reprocessed claims, and appeals. Every deactivated code keeps its page here, clearly marked, with the replacement code when X12 names one.