CO-21: Required Authorization Not Obtained
CO (Contractual Obligation)What is CO-21?
CO-21 is a Contractual Obligation code indicating the required authorization was not obtained for the service. This is functionally similar to CO-197 but some payers use CO-21 specifically for services where authorization was expected but no auth number was found on file.
Why Does CO-21 Occur?
- Prior authorization not obtained before the service.
- Authorization number not included on the claim.
- Authorization expired before the service date.
- Authorization was for a different procedure or provider than what was billed.
How to Fix CO-21 Denials
- Verify whether prior auth was obtained and if the auth number was included on the claim.
- If auth exists but was not on the claim, add the auth number and resubmit.
- If auth expired, check whether the payer allows retroactive authorization.
- Appeal with clinical documentation and the auth reference if the payer's records are incorrect.
CO-21 by Payer
| Payer | Common RARC | Appeal Deadline | Notes |
|---|---|---|---|
| UnitedHealthcare | Varies | 60 days from remittance | Reconsideration required before formal appeal. |
| Anthem | Varies | 365 days from denial notice | Check state-specific provider manual for variations. |
| Aetna | Varies | 180 days from denial | Strict in-network filing enforcement. |
| Cigna | Varies | 180 days from denial | Cigna COB team: 1-800-244-6224. |
| Medicare | Varies | 120 days (redetermination at MAC) | Five levels of appeal starting with MAC redetermination. |
Related CARC Codes
If you are seeing CO-21, check these related codes: CO-197 (precertification absent), CO-23 (prior auth not obtained), CO-21 (authorization absent).
Common Questions About CO-21
What does CO-21 mean?
CO-21 indicates required authorization not obtained. Check the RARC code on the EOB for the specific reason and follow the resolution steps above.
Can I appeal a CO-21 denial?
Yes. Commercial payers allow 60-365 days to appeal depending on the payer. Gather supporting documentation before filing. Medicare allows 120 days for a redetermination request.
Altair catches CO-21 denials before submission with authorization tracking. See how pre-submit claim scoring works.