CARC and RARC are two of the core code sets used in healthcare claims adjudication. They explain why a claim was paid, denied, or adjusted. Your search results confirm this across multiple authoritative sources. CARCs explain the reason for a financial adjustment on a claim or service line. They tell you why the payer changed the billed amount (denied, reduced, bundled, not covered, etc.). They appear on ERAs (Electronic Remittance Advice) and EOBs. They are standardized across the industry and maintained by X12. Remittance Advice Remark Codes (RARCs) are used to provide additional explanation for an adjustment already described by a Claim Adjustment Reason Code (CARC) or to convey information about remittance processing. Each RARC identifies a specific message as shown in the Remittance Advice Remark Code List. There are two types of RARCs, supplemental and informational. The majority of the RARCs are supplemental; these are generally referred to as RARCs without further distinction. Supplemental RARCs provide additional explanation for an adjustment already described by a CARC. The second type of RARC is informational.