CO-15 Denial Code: Authorization Number Missing or Invalid

The CO-15 denial code means the authorization number is missing, invalid, or does not apply to the billed service or provider. The payer is not necessarily saying the service lacked authorization — it is saying the number on the claim is absent, wrong, or attached to the wrong service. That distinction matters, because a service that was properly authorized can still draw a CO-15 from a simple data error in the auth field.

What is the CO-15 denial code? CO-15 is a Claim Adjustment Reason Code (CARC) indicating the authorization number is missing, invalid, or does not apply to the billed services or provider, applied under the Contractual Obligation group as a provider write-off until corrected.

Undeny's Take

CO-15 splits cleanly into two very different problems, and treating them the same is how the appealable ones get written off. The first is a clerical miss: the authorization existed, but the number was left off the claim, keyed wrong, or tied to a different service or provider than the one billed — these are corrected-claim fixes, not appeals. The second is the real gap: no authorization was obtained when the payer required one, which is a harder argument needing a retro-authorization or a medical-necessity case. Before you assume the worst, pull the auth on file and compare it line by line to the claim — service, provider, dates, units. Most CO-15 denials are the clerical kind wearing the costume of the serious kind.

What CO-15 Means

CO-15 reports an authorization problem on the claim: the number is missing entirely, fails validation, or does not match the service, provider, or date range it was issued for. Many payers require prior authorization or precertification for specific services, and the claim must carry a valid, matching authorization number. Under the Contractual Obligation group, the amount is the provider's responsibility until the authorization issue is resolved, not a patient charge.

Why the Authorization Fails

The authorization number was left off the claim or entered incorrectly.
The number on file applies to a different service, provider, or date than the one billed.
The authorized units or visit count were exceeded by the claim.
No prior authorization was obtained for a service the payer required it for.

How to Fix a CO-15

Pull the authorization on file and confirm whether one exists for this service, provider, and date.
Compare the authorization details — service, units, dates, rendering provider — against the claim line by line.
If a valid authorization exists, correct the number or matching details on the claim and refile.
If no authorization was obtained, request a retroactive authorization or appeal on medical necessity with the appeal generator.

Related Codes

CO-15 is related to CO-16 (claim lacks information needed for adjudication) and CO-197 (precertification or authorization absent). Browse the full set under denial codes.

Frequently Asked Questions

What does CO-15 mean?

CO-15 means the authorization number on the claim is missing, invalid, or does not apply to the billed service or provider. It points to a problem with the authorization data, which may be a clerical error or a genuine missing authorization.

Is CO-15 always a missing authorization?

No. Often the authorization exists but the number was omitted, mistyped, or matched to the wrong service or provider. Compare the authorization on file to the claim before concluding that no authorization was obtained.

Can I bill the patient for a CO-15?

No. CO-15 carries the Contractual Obligation group, so the amount is a provider write-off until the authorization issue is corrected. Fix the number or obtain authorization rather than billing the patient.

How is CO-15 different from CO-197?

CO-15 focuses on an authorization number that is missing, invalid, or mismatched, while CO-197 indicates precertification or authorization was absent altogether. They overlap, but CO-15 often points to a correctable data error on an existing authorization.

Informational only — not legal, medical, or billing advice. Always verify against current payer authorization requirements.

Fix CO-15 denials automatically

Undeny tells you whether a CO-15 is a data fix or a missing authorization and drafts the response. Generate an appeal · Browse denial codes