Decode your claim denials and find out what to do next

A CARC (Claim Adjustment Reason Code) explains why a payer adjusted or denied a claim. It’s the primary code that tells you the reason for the denial, such as a duplicate claim, an authorization issue, or a coordination of benefits problem. A RARC (Remittance Advice Remark Code) provides additional context or clarification to go along with the CARC. Think of the CARC as the reason and the RARC as the explanation. You’ll find both on your EOB or ERA. Some denials include only a CARC; others include a CARC plus one or more RARCs that help you understand what action to take.

CO-16 means the claim is missing information or has a submission or billing error that prevents processing. It’s one of the most common denial codes in behavioral health and is almost always correctable. The fix depends on what’s missing: it could be a missing diagnosis code, an incomplete NPI, a date of service mismatch, or a required modifier that wasn’t included. CO-16 is usually accompanied by one or more RARC codes (often N30, N265, or MA04) that point more specifically to what needs to be corrected. In most cases, this denial is worth correcting and resubmitting rather than appealing.

Timely filing limits for appeals vary by payer and plan type. Most commercial payers allow 30 to 180 days from the date of the denial to file an appeal. Medicare appeals for Part B claims generally give you 120 days from the date of the remittance notice to file a redetermination request. Medicaid timelines vary by state, but 60 to 90 days is common. For all payers, the safest approach is to start the appeal process as soon as possible after receiving the denial, ideally within 30 days. Always check the payer-specific timely filing policy in your provider manual, and document every step of the appeal process with dates and confirmation numbers.

The denial codes most worth appealing are those caused by fixable errors or missing documentation rather than contract limitations. CO-4 (modifier issue), CO-16 (missing or invalid information), CO-97 (bundling), and CO-22 (coordination of benefits) are frequently worth resubmitting or appealing because the underlying issue can usually be resolved. PR-1 (deductible) and PR-2 (coinsurance) are typically not appealable since they represent patient responsibility. CO-45 (charge exceeds fee schedule) is a contractual adjustment and generally can’t be appealed. When in doubt, look at the CARC category prefix: CO denials are often correctable, OA denials may require additional context, and PR denials usually shift responsibility to the patient.

A clean claim rate is the percentage of claims you submit that are accepted and processed on the first pass without requiring correction or resubmission. In behavioral health, a clean claim rate above 95% is considered strong. Rates below 90% indicate systematic billing problems that are likely costing you real money in delayed payments and staff time spent on rework. Clean claim rate is one of the most important leading indicators of your billing operation’s health, because every claim that doesn’t go through clean has to be touched again, which multiplies your cost per claim and slows your cash flow.

Start by categorizing your denials by CARC code each week. If the same codes appear repeatedly, especially CO-4, CO-16, or CO-97, you have a systemic process issue rather than random errors. Once you know which codes account for the most denials by volume and dollar amount, you can trace them back to a root cause: a documentation gap, a payer rule you weren’t following, or a front desk verification step that’s being skipped. Fix that root cause and the denial rate drops at the source. Most practices that actively manage denial data see measurable improvement within 60 to 90 days.