CO-15 Denial Code: Missing or invalid authorization number (deactivated code)
The authorization number is missing, invalid, or does not apply to the billed services. Note: X12 officially deactivated CARC 15 effective 05/01/2018 — compliant payers now use CO-197 (authorization absent), CO-198 (authorization exceeded), or CO-16 with a remark code instead. If you're still receiving CO-15, the payer's system is using retired codes; work it like an authorization denial.
Why CO-15 happens
- ●Payer running an outdated adjudication system that still emits retired CARC 15
- ●Prior authorization obtained but not entered on the claim
- ●Auth number entered in the wrong field or with typos
- ●Authorization covers different CPT codes or dates of service
How to fix a CO-15 denial
- 1
Locate the authorization and confirm codes/dates match services billed
- 2
Add the auth number to the claim (Box 23 / 2300 REF*G1) and resubmit
- 3
If services changed, request a retro-authorization or updated auth
- 4
Check the payer's companion guide — current denials for the same issue arrive as CO-197 or CO-198
How to prevent it
Verify auth requirements at scheduling and validate auth-to-claim match pre-submission.
Drowning in CO-15 denials?
OakClaim works every denial within 48 hours and builds prevention rules so they stop recurring.