Medical Billing Denial Code Lookup

Complete reference for Claim Adjustment Reason Codes (CARC) and Remittance Advice Remark Codes (RARC) used in ANSI X12 835 Electronic Remittance Advice files. CARC codes identify why a claim or service line was adjusted. RARC codes provide supplemental explanation. Both code sets are maintained by the Washington Publishing Company under CMS oversight and updated quarterly. Each entry includes the official WPC definition, common billing causes, appeal strategy, and applicable regulatory citations.

High-volume CARC codes: CO-4 (service inconsistent with modifier — appeal with modifier justification and CMS NCCI edit documentation), CO-11 (diagnosis inconsistent with procedure — verify ICD-10/CPT pairing and LCD coverage), CO-16 (claim lacks information — identify missing element from RARC and resubmit), CO-22 (coordination of benefits — obtain primary EOB and rebill), CO-29 (timely filing — appeal with proof of timely submission; not recoverable if window passed), CO-45 (contractual adjustment — verify contracted rate against fee schedule), CO-96 (non-covered charge — verify benefit exclusion before writing off), CO-97 (service included in allowance for another service — NCCI bundling; appeal with modifier or medical necessity for separate billing).

High-volume RARC codes: MA01 (appeal rights notice), MA04 (secondary claim required), MA130 (missing or invalid information — cross-reference with CO-16), N130 (claim submitted to wrong payer), N570 (missing/incomplete/invalid credentialing data), N265 (claim submitted without prior authorization), N290 (missing prior authorization number).

• Denial Decoder — step-by-step appeal paths for each code
• Appeal Letter Builder — regulatory-cited letters from denial codes
• Pre-written appeal templates by denial category