CO-109 denial code
This claim is not payable by this payer or contractor. You sent it to the wrong place.
CO — Contractual Obligation. The write-off is yours. You agreed to it in your contract with the payer, and you cannot bill the patient for it.
Why you got it
- 1The patient is enrolled in a Medicare Advantage plan, and the claim went to traditional Medicare.
- 2The service is covered by a different contractor or a different jurisdiction.
- 3The patient has other primary insurance and Medicare is secondary.
How do I fix a CO-109 denial?
- Verify eligibility and find out who the correct payer actually is, then submit there.
- Watch the timely filing clock. It is running for the correct payer, and it has been running the whole time you were waiting on this denial.
How to stop the next one
This is an eligibility problem, and eligibility is checkable before the visit rather than after the denial.
Our diagnosis scrubber will not catch this one. CO-109 is driven by procedure codes, modifiers, or eligibility rather than by the diagnosis set — and procedure-side checking needs an AMA CPT licence we do not hold yet. We would rather tell you that than sell you a tool that quietly misses your most common denial.
If denials like this are a volume problem rather than a one-off, the denial management page explains how the paid workspace catches the coding causes on every claim, and the free ICD-10-CM lookup shows the coding notes behind any diagnosis code on the remittance.