The official definition
“Claim/service not covered by this payer/contractor. You must send the claim/service to the correct payer/contractor”
That is the verbatim definition of CARC 109 from the X12 Claim Adjustment Reason Code set, the standardized codes every insurer uses on EOBs and remittance advices. The letters in front of the number are the group code. CO: Contractual Obligation: an adjustment between the provider and the insurer. An in-network provider should not bill you for CO amounts.
What it means in plain English
The claim went to the wrong insurance company. Not denied on the merits; just delivered to the wrong address. Common around plan switches, dual coverage, Medicare transitions, and injuries that belong with workers' comp or auto insurance instead of health insurance.
What to check on your EOB
- Which insurer should have received the claim; check your current card and any other applicable coverage.
- Whether the service relates to a work injury or car accident; those route to workers' comp or auto coverage first.
What to do next
- Give the provider the correct insurance information and ask them to rebill the right payer.
- Watch the timely-filing clock: the provider should rebill promptly, and a late rebill after their own misdirection is not your bill to pay.
Who's responsible
Provider, with your correct coverage info. Most denials carry a clear owner. Knowing whether the fix belongs to you, your doctor, or the billing office is half the battle. If it's the provider's error, you should not be paying for it.
Want the fundamentals first? Start with how to read an EOB and the 7 most common billing errors. This page is general information about standardized denial codes, not legal or medical advice.
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