CARC
Claim Adjustment Reason Code, the externally maintained code list explaining 835 payment adjustments.
Definition
CARCs explain at line level why a paid amount differs from the billed amount — for example 1 (deductible), 2 (coinsurance), 45 (charge exceeds allowed amount), 96 (non-covered charge). They live in the CAS segment of the 835 and are often paired with a RARC for extra detail.
Origin
CARC is an external code list maintained for ASC X12 by WPC (Washington Publishing Company), updated three times a year; its use is mandated by HIPAA through the 835 TR3 (005010X221).
Example in context
In CAS*PR*1*250.00~ the CARC 1 tells the provider that 250.00 is patient responsibility because it was applied to the deductible.