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CO-15 Denial Code (Deactivated): Authorization Number

CO-15 meant the authorization number on the claim was missing, invalid, or did not apply to the billed service or provider. X12 deactivated it, and payers now report these problems with more specific authorization codes such as 197, 284, and 296.

X12 deactivated CARC15 on May 1, 2018. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Quick facts

Code
CO-15 (CARC 15)
Status
Deactivated StoppedMay 1, 2018 (in use since January 1, 1995).
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The provider was held responsible because the authorization problem was a billing or process issue, not a patient liability.
Official description
The authorization number is missing, invalid, or does not apply to the billed services or provider.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-15 meant

CARC 15 told the provider that the payer could not match the claim to a usable authorization. There were three ways that could happen: the authorization number was left off the claim, the number reported was not recognized as valid, or the number was real but covered different services or a different provider than the one billing.

Because one code covered all three problems, billers often had to call the payer just to learn which one applied.

What replaced it

X12 did not name a single successor in the code’s text, but the active code set now splits the scenarios apart:

  • CO-197 when precertification or authorization is absent.
  • CO-284 when a number may be valid but does not apply to the billed services.
  • CO-296 when a number may be valid but does not apply to the billing provider.
  • CO-198 when the authorized amount was exceeded.

Which of these a payer uses for a given situation depends on the payer, so read any accompanying remark code.

If you still see CO-15

You may run into CO-15 on archived remittances, in old denial reports, or in a practice management system that never refreshed its code table. If a current ERA shows it, ask the payer which authorization issue they meant and whether they will reissue the adjustment with an active code.

To resolve the claim itself, pull the authorization record from the payer portal and compare the number, dates, service codes, units, and rendering provider to what was billed. Correct the claim and resubmit it as a corrected claim, or request a retroactive authorization if the payer allows one. Post any final write-off as a contractual adjustment rather than transferring it to the patient.

  • CO-197 (Precertification/authorization/notification/pre-treatment absent.): Used today when no precertification or authorization was obtained at all.
  • CO-284 (Precertification/authorization/notification/pre-treatment number may be valid but does not apply to the billed services.): The authorization number may be valid but does not match the services billed.
  • CO-296 (Precertification/authorization/notification/pre-treatment number may be valid but does not apply to the provider.): The authorization number may be valid but does not match the provider billed.
  • CO-198 (Precertification/notification/authorization/pre-treatment exceeded.): Authorization existed but the approved units or visits were exceeded.

CO-15 FAQ

Why was CO-15 retired?

It bundled three different situations into one code: no authorization number, a bad number, and a number that belonged to other services or another provider. The newer codes separate those cases so the fix is clearer.

Can I bill the patient for a CO-15 adjustment?

Generally no. The CO group placed the amount on the provider, because obtaining and reporting authorization is normally the provider's job.