CO-22 denial code
The payer believes another insurer should pay first. This is a coordination-of-benefits denial: they are not saying the service isn't covered — they are saying they are not the one who covers it first, and they want the other payer's answer before giving theirs.
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 has other coverage that is primary: a working spouse's plan, an employer plan alongside Medicare, or Medicare Advantage when the claim went to traditional Medicare.
- 2The visit is accident-related, so auto, liability, or workers' compensation coverage comes first.
- 3The payer's coordination-of-benefits records are stale — the other coverage ended years ago, but nobody told them.
- 4The patient never answered the payer's COB questionnaire, so the payer defaulted to 'someone else is primary'.
How do I fix a CO-22 denial?
- Verify eligibility and ask specifically about other coverage. The order of payers is determined by rules (employment status, birthday rule for dependents, accident type), not by whichever card the patient handed you.
- If another payer really is primary, bill them first, then resubmit here with the primary's remittance attached.
- If there is no other coverage, the patient usually has to say so themselves — have them call the payer and update their COB record. Payers routinely refuse to take the provider's word for it.
How to stop the next one
Ask about other coverage and accident involvement at check-in, every time. The COB question takes thirty seconds at the desk and thirty days on a remit. You may also see this with a PR prefix (PR-22) when the payer assigns the sorting-out to the patient.
Our diagnosis scrubber will not catch this one. CO-22 is driven by procedure codes, modifiers, or eligibility rather than by the diagnosis set — and procedure-side checking needs CPT codes, which aren’t included 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.