Interpret CARC and RARC remark codes from an 835 ERA denial and route claims to the correct denial management workflow

Verified steps

1. Extract CAS segments from the 835 835 service line (Loop 2110) and claim level: CAS01 is the adjustment group code (CO = contractual, PR = patient responsibility, OA = other adjustment, PI = payer-initiated), CAS02 is the CARC (Claim Adjustment Reason Code), CAS03 is the adjustment dollar amount; a single CAS segment can carry up to three CARC/amount pairs
2. Look up each CARC in the current X12/CMS CARC code list (published by CMS and X12 jointly, updated quarterly); common actionable codes include 4 (late filing), 16 (claim lacks required information), 18 (duplicate), 97 (not covered — requires auth), 109 (claim not covered by this payer)
3. Read MOA and LQ/HI segments or the remittance remark code (N1 through NX prefix codes) in the 835 for RARC codes; RARC provides additional context on the reason for the CARC adjustment — look up in the RARC code list maintained by CMS
4. Classify denials by root cause using the CARC/RARC combination: coding denial (CARCs 4, 11, 16, 97) → clinical/coding team; eligibility denial (CARC 27, 109) → eligibility re-verification; duplicate (CARC 18) → claim deduplication review; PR codes → patient billing
5. For denials with a viable appeal path, generate an appeal packet with the original claim, supporting documentation, CARC/RARC explanation, and clinical notes; submit within the payer's appeal window (typically 60–180 days from the remittance date)
6. Track denial rates by CARC code over time in your analytics layer to identify systemic billing issues (e.g., consistent CARC 16 for a specific CPT code indicating a documentation gap)