Short answer: Most denials trace back to seven claim adjustment reason codes. Missing information (CO-16), missing authorization (CO-197), medical necessity (CO-50), bundling (CO-97), coordination of benefits (CO-22), timely filing (CO-29) and non covered services (PR-204). Nearly all are preventable before the claim is sent.
How to read a denial code
Every denial on an 835 remittance carries a group code and a claim adjustment reason code (CARC). The group code says who owns the balance: CO (contractual obligation, the provider absorbs it), PR (patient responsibility), OA (other adjustment) or PI (payer initiated). The CARC number says why. Remittance advice remark codes (RARCs) add detail.
The seven codes
| Code | What it means | The front end fix |
|---|---|---|
| CO-16 | Claim lacks information or has submission or billing errors | Scrub claims against payer edits; check the RARC for the missing field (NPI, modifier, referring provider) |
| CO-197 | Precertification or authorization absent | Track authorizations by CPT code and payer before scheduling; attach the auth number to the encounter |
| CO-50 | Not deemed a medical necessity by the payer | Match ICD 10 codes to the payer's coverage policy; document medical necessity in the note |
| CO-97 | Service included in payment for another service already adjudicated | Check NCCI edits; use modifiers 25 or 59 only when documentation supports a distinct service |
| CO-22 | Care may be covered by another payer (coordination of benefits) | Confirm primary and secondary coverage at every visit; update COB with the patient |
| CO-29 | Time limit for filing has expired | Submit daily; monitor clearinghouse rejections so rejected claims are fixed before the filing window closes |
| PR-204 | Service not covered under the patient's current benefit plan | Verify benefits before the visit; obtain a signed financial waiver or ABN where appropriate |
A prevention checklist
- Verify eligibility and benefits two business days before every visit.
- Log prior authorizations by payer and CPT code, with expiry dates.
- Scrub every claim against payer specific edits before submission.
- Work clearinghouse rejections daily, not weekly.
- Categorize every denial by root cause and review the top five monthly.
Practices that work denials within 48 hours and fix the root cause typically see their denial rate fall within one or two billing cycles. Our KPI guide shows the benchmarks to track.
