Insurance denial codes, decoded
UPDATED JULY 2026 · U.S. PLANS · NOT LEGAL OR MEDICAL ADVICE
The codes on your EOB or denial letter (CO-45, CO-50, PR-204…) are standardized Claim Adjustment Reason Codes. Each one tells you who is expected to act — you, or the provider’s billing office — and whether an appeal is worth it. Find yours below.
How to read a code
- CO (Contractual Obligation): in-network providers generally cannot bill you for these adjustments.
- PR (Patient Responsibility): assigned to you — but verify before paying.
- OA (Other Adjustment): usually informational.
| Code | What it means | Appeal? |
|---|---|---|
| CO-4 | Procedure code inconsistent with the modifier | Rarely |
| CO-11 | Diagnosis inconsistent with the procedure | Rarely |
| CO-15 | Authorization number missing or invalid | Sometimes |
| CO-16 | Claim lacks information or has a submission error | Rarely |
| CO-18 | Duplicate claim or service | Rarely |
| CO-22 | Care may be covered by another payer (coordination of benefits) | Sometimes |
| CO-26 | Expenses incurred before coverage began | Sometimes |
| CO-27 | Expenses incurred after coverage ended | Sometimes |
| CO-29 | Timely filing limit expired | Sometimes |
| CO-45 | Charge exceeds the contracted fee schedule | Rarely |
| CO-50 | Not deemed medically necessary | Yes |
| CO-96 | Non-covered charges | Sometimes |
| CO-97 | Payment included in another billed service (bundled) | Rarely |
| CO-109 | Claim not covered by this payer — submit elsewhere | Rarely |
| CO-119 | Benefit maximum reached | Sometimes |
| CO-151 | Frequency of services not supported | Yes |
| CO-167 | Diagnosis not covered | Yes |
| CO-197 | Precertification / prior authorization absent | Yes |
| CO-198 | Precertification exceeded (more visits/units than authorized) | Yes |
| CO-204 | Service not covered under the current benefit plan | Yes |
| CO-231 | Mutually exclusive procedures | Rarely |
| CO-234 | Procedure not paid separately | Rarely |
| CO-236 | Procedure/modifier combination not compatible | Rarely |
| CO-242 | Services not provided by network providers | Yes |
| CO-243 | Services not authorized by network/primary care providers | Sometimes |
| CO-252 | Attachment or documentation required | Rarely |
| CO-B7 | Provider not certified/eligible to be paid for this service | Rarely |
| CO-B15 | Required qualifying service/procedure missing | Rarely |
| OA-23 | Impact of prior payer adjudication | Rarely |
| PR-1 | Deductible | Rarely |
| PR-2 | Coinsurance | Rarely |
| PR-3 | Copayment | Rarely |
| PR-31 | Patient cannot be identified as insured | Sometimes |
| PR-33 | Insured has no dependent coverage | Sometimes |
| PR-49 | Routine/preventive exam not covered | Sometimes |
| PR-96 | Non-covered charges (patient responsibility) | Yes |
| PR-204 | Service/drug not covered under the current plan (patient billed) | Yes |
Don’t see your code? The letter must still explain the denial in words and state your appeal rights — start with the step-by-step appeal guide.
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