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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.

CO-15 was deactivated by X12 on 2018-05-01

It is no longer an active reason code on X12's own list, so a remittance quoting it today is using a retired code — not unusual, since payer systems can lag a deactivation by years, but worth knowing before you work it as though it were current. The meaning below is what the code meant while it was active, for exactly that reason. Check the current X12 list for the code that replaced it on new remittances.

Read the group code before you act on this

15 is the reason. The CO in front of it is the group code, a separate field on the remittance, and it is the one that decides who owes the money: 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. You may not bill the patient. What the other group codes mean.

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.

A denial like this one is the recurring cost that medical billing outsourcing is built to take off your desk — a dedicated seat working the queue instead of it waiting for whoever has a free hour.

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-198 — Authorization limit exceeded
CO-288 — Referral 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) — before any of it is recovered, and whether or not it ever is.

Payers ultimately pay roughly 90% of claims even while using an initial denial to slow payment (source), so the reason one sits is rarely that nobody knows how to work it. Put your own denial count in.

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 2026-09-14. 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 updated 2026-09-14

Code descriptions are the standard published text. Everything after them is operational guidance on how the work is done, and payer policy governs any individual claim.

Other denial codes

Next step

Is CO-15 one of the denials costing you most?

Send a ninety-day denial report and an aged AR summary, with no patient identifiers. Within two working days you get a written summary of which denial reasons are costing you most and what is recoverable.

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