Claim adjustment reason code (CARC)

A CARC is the payer’s reason, in code. Whenever a payer pays a line for less than the billed amount, including paying nothing, the remittance has to account for the difference, and it does so with one or more adjustments. Each adjustment carries a group code, a CARC and an amount. The group code says who absorbs the amount: CO for a contractual obligation the provider writes off, PR for patient responsibility, OA for other adjustments, and PI for payer-initiated reductions. The CARC says why: the service was not covered, the authorization was missing, the claim duplicated another, the charge exceeded the fee schedule, the deductible applied. X12 publishes the list among its external code sets and describes the codes as explaining why a claim or service line was paid differently than it was billed, so the same code means the same thing across Medicare, Medicaid plans and commercial carriers.

CARCs matter because they are the input to denial management and to posting rules. A posting system decides from the group code and CARC whether an amount is a write-off, a patient balance or a denial to be worked. Denial reports group by CARC to show whether the problem is eligibility, authorization, coding or timely filing. Underpayment reports look for contractual adjustments that are larger than the contract allows.

The mistake is reading the CARC alone. Many CARCs are deliberately broad, and the specifics live in the remittance advice remark codes that travel with them. A CARC that says the claim lacks information needed for adjudication tells you almost nothing until you read the RARC that names the missing element. Read both, and check the payer’s companion guide, because some payers map their internal reasons onto generic CARCs.