CO-15 Denial Code: Missing, Invalid, or Inapplicable Authorization Number

What does denial code CO-15 mean?

CO-15 means the authorization number is missing, invalid, or does not apply to the billed services or provider. Read that carefully: the payer is not necessarily saying you never got an auth. It is saying the number on the claim, or the absence of one, does not line up with an authorization in its system for this patient, this service, this provider, and these dates.

Example ERA line: MRI lumbar spine, CPT 72148, billed $1,450.00, allowed $0.00, CO-15 $1,450.00, paid $0.00. The auth was approved under the ordering group's TIN, but the claim went out under the imaging center's NPI, so the number "does not apply to the billed provider."

Why did the claim get a CO-15?

• Auth number omitted or fat-fingered in the 2300 REF*G1 segment (box 23 on the CMS-1500).
• Auth issued for different CPT codes than what was actually performed; the radiologist added a with-contrast sequence, the auth covered without.
• Wrong provider or facility on the auth, a constant problem when services are scheduled at a different location than where the auth was requested.
• Date of service outside the auth window. Rescheduled procedures are the classic trap; the auth expired before the new date.
• Units exhausted, which some payers code as CO-15 rather than CO-198.

How do you fix and resubmit a CO-15 denial?

1. Pull the original authorization from the payer portal. Compare five fields against the claim: auth number, CPT codes, provider NPI/TIN, facility, and date range.
2. If the number was missing or mistyped, add it and resubmit a corrected claim. Done.
3. If the CPT, provider, or dates do not match, call the payer's UM department and ask them to amend the existing auth. Many will backdate or add a code to an active auth; almost none will create a new auth after the fact.
4. Resubmit once the amended auth shows in the portal, and reference the call ticket number in your notes.

How do you prevent CO-15 denials?

Build a pre-claim auth match step: before any authorized service bills out, someone verifies that the auth number, CPTs, provider, and dates on the claim mirror the auth exactly. Practices that add this check to their scrubber rules or front-end workflow typically cut auth denials by more than half. Track auth expiration dates on rescheduled procedures, and make prior authorization verification part of the check-in script for high-dollar services.

Can you appeal a CO-15 denial?

Yes, and you should whenever a valid authorization existed for the service. Attach the auth approval letter or a portal screenshot showing the auth number, approved codes, and date range, plus the claim. That documentation wins the majority of CO-15 appeals because it proves payer error or an administrative mismatch. Draft it in minutes with the appeal letter generator and confirm your filing window with the appeal deadline calculator before the queue eats the deadline.