CO-11 Denial Code: Diagnosis Doesn't Match Procedure
The official definition
“The diagnosis is inconsistent with the procedure”
That is the verbatim definition of CARC 11 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 diagnosis code (what's wrong with you) doesn't line up with the procedure code (what was done about it) according to the insurer's coding logic. Nine times out of ten this is a provider coding issue: a non-specific diagnosis code, or a diagnosis entered on the wrong line of a multi-service claim.
What to check on your EOB
- The diagnosis and procedure descriptions on your EOB: do they describe the visit you actually had?
- Whether the claim covered multiple services. Diagnosis codes attached to the wrong line item are a common trigger.
What to do next
- Contact the provider's billing office and ask them to review the diagnosis-procedure pairing.
- The provider may need a more specific diagnosis code that supports the procedure, then a corrected resubmission.
- If the codes are correct as billed, the provider should appeal with clinical documentation.
Who's responsible
Provider. 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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