Denial code CO-4 (CARC)

CARC CO-4 (contractual obligation) often appears when the payer adjusts a charge based on a contract between the insurer and the provider. A code on your EOB or denial letter explaining why a claim was not paid or was reduced. Standard codes are CARC (Claim Adjustment Reason Codes) and RARC (Remittance Advice Remark Codes). Payer-specific codes vary by insurer.