EOB Denial Codes Explained

CARC Codes: The Primary Denial Reason

Claim Adjustment Reason Codes appear on every EOB and electronic remittance advice. Each code maps to a specific denial category maintained by the Washington Publishing Company. When you see CO-50 on a line item, the payer denied it for medical necessity. CO-97 means bundling. CO-29 means timely filing. Identifying the CARC code is the first step in every appeal because it tells you what documentation and argument you need.

RARC Codes: The Supplemental Detail

Remittance Advice Remark Codes add context to the CARC code. A CARC 50 denial might carry RARC N130 citing a specific medical policy, or RARC M15 indicating frequency limits were exceeded. RARC codes help you pinpoint the exact payer rule applied to your claim so your appeal can address that specific rule rather than the general denial category.

Most Common EOB Denial Codes

• CARC 50 — Not medically necessary per payer policy
• CARC 97 — Service bundled into another procedure payment
• CARC 29 — Claim filed after the timely filing deadline
• CARC 197 — Prior authorization or precertification missing
• CARC 4 — Modifier missing, invalid, or inconsistent with procedure

From Code to Appeal Action

Once you identify the CARC code, match it to the correct appeal strategy and documentation checklist. Medical necessity denials need clinical records. Bundling denials need operative notes. Timely filing denials need submission proof. Every code has a defined appeal path — the code itself is your roadmap to recovered revenue.