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Claim adjustment reason code

CO-15: Authorization number missing or invalid

CO-15 means: The authorization number is missing, invalid, or does not apply to the billed services or provider. There is an authorization requirement here, and the number you sent is absent, wrong, or does not cover what was billed.

Read the group code before you act on this

15 is the claim adjustment reason code. The CO in front of it is the group code — a separate field the payer sets on the remittance. The same reason code arrives under different group codes depending on the payer and the situation, and the group code, not the reason code, decides who owes the money.

CO — contractual obligation. You write it off. You may not bill the patient.
PR — patient responsibility. Billable to the patient.
OA — other adjustment, and PI — payer initiated reduction. Neither is patient responsibility.

What causes it

Authorization obtained but never entered on the claim
Number transposed at charge entry
Authorization covers a different code, a different provider, or a different date range than the service
Units billed exceed the units authorized

How to work it

Pull the authorization and compare four things against the claim: code, provider, date range and units. One of them will not match.
If it is a data entry problem, correct and resubmit as a corrected claim.
If the authorization genuinely does not cover the service, ask the payer whether a retro-authorization is possible and on what timeline.
Log the authorization number, expiry and unit count on the account so the next claim in the course does not repeat it.

How to stop it recurring

Record the authorized code, provider, date range and unit count at the time it is granted, and check the remaining units before each subsequent visit rather than at the end.

Who does this work

A prior authorization seat at $1,900 per seat per month works this queue full time, during your business hours, inside your own system. Every call is logged with the payer reference number and the outcome, and every Friday you get it in writing.

What that seat does →

Codes worked the same way

CO-15 is taken back to the authorization. So are these, which is why a queue sorted by recovery route moves faster than one sorted by code number — the same person, in the same system, with the same evidence to hand, clears all of them in one pass.

CO-197 — Prior authorization absent
CO-39 — Authorization already refused
CO-272 — Coverage guidelines not met
N54 — Claim does not match the authorization

Specialties that name this among their costliest

These are specialties whose own worst denials include one of this kind. The line under each is the denial they name, quoted from their page so you can see what the link is based on.

Ambulatory Surgery Centers
Prior authorization obtained for the surgeon but not the facility
Behavioral Health
Authorization units exhausted mid-course without renewal
Urology
Prior authorization missing for advanced imaging
Radiology
Advanced imaging denied for missing prior authorization
Ophthalmology
An injection given after the drug authorization lapsed, or under an authorization written for a different agent than the one actually drawn up that day.
Neurology
Long-term video EEG authorized as an ambulatory home recording but performed as an admission to the epilepsy monitoring unit, so the facility days sit outside the authorization

What leaving it costs

Working a denied claim costs $57.23 per denied claim in administrative time. Source. At 100 denials a month — an illustration, not a measurement of your practice — that is $5,723 a month, or $68,676 a year, in labour alone.

The figure that makes it worth spending: about 90% of initially denied claims are eventually paid. Source. The reason a denial sits is almost never that nobody knows how to work it — it is that nobody has the hours.

Questions

What does denial code CO-15 mean?

The authorization number is missing, invalid, or does not apply to the billed services or provider. In plain terms: There is an authorization requirement here, and the number you sent is absent, wrong, or does not cover what was billed.

What causes CO-15?

Authorization obtained but never entered on the claim. Number transposed at charge entry. Authorization covers a different code, a different provider, or a different date range than the service. Units billed exceed the units authorized.

How do you fix a CO-15 denial?

Pull the authorization and compare four things against the claim: code, provider, date range and units. One of them will not match.. If it is a data entry problem, correct and resubmit as a corrected claim.. If the authorization genuinely does not cover the service, ask the payer whether a retro-authorization is possible and on what timeline.. Log the authorization number, expiry and unit count on the account so the next claim in the course does not repeat it..

Can CO-15 be prevented?

Record the authorized code, provider, date range and unit count at the time it is granted, and check the remaining units before each subsequent visit rather than at the end.

Is CO-15 the same as PR-15?

Same reason, different group code. The number 15 is the reason: There is an authorization requirement here, and the number you sent is absent, wrong, or does not cover what was billed. The prefix says who carries the amount. CO means contractual obligation — the payer says the amount is not billable to anybody, and it is written off unless the denial itself is overturned. PR-15 is the same reason assigned to patient responsibility — the payer says the amount is owed by the patient, and it is billed to them. Read the prefix before the number: it decides whether you appeal, write off, or bill the patient.

What is the difference between CO-15 and CO-16?

CO-15: There is an authorization requirement here, and the number you sent is absent, wrong, or does not cover what was billed. CO-16: Something on the claim is missing or malformed. On its own the code tells you nothing — the detail is in the remark code that comes with it. They are different reasons that happen to sit next to each other in the list, and they are worked differently — CO-15 is taken back to the authorization; CO-16 is corrected and resubmitted.

Code descriptions are the standard X12 claim adjustment reason and remittance advice remark code text. Payer policies differ, and the payer’s own coverage policy governs any individual claim. This page is working guidance, not legal or clinical advice.

Last updated 2026-09-12. This is operational guidance drawn from payer remittance practice, not legal, coding or reimbursement advice. Payer-specific rules vary and change; confirm against the payer’s own policy before acting on a specific claim.

Written by Ibtesam Asif · Last reviewed 2026-09-12

Code descriptions are the standard published text. Everything after them is operational guidance from our own work, and payer policy governs any individual claim.

Other denial codes

Next step

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