CO-236 Denial Code: Same-Day Procedure Conflict (NCCI)
The official definition
“This procedure or procedure/modifier combination is not compatible with another procedure or procedure/modifier combination provided on the same day according to the National Correct Coding Initiative or workers compensation state regulations/fee schedule requirements”
That is the verbatim definition of CARC 236 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
Two procedures billed for the same day aren't allowed together under the National Correct Coding Initiative, the federal rulebook of code combinations. Usually one code already includes the other, so this denial is the system catching a billing conflict, not judging your care. The provider either billed incorrectly or needs to justify why the procedures were genuinely separate.
What to check on your EOB
- Whether you're being billed for the denied line; an in-network provider generally shouldn't pass an NCCI conflict to you.
- Whether the procedures really were distinct (different sites, different sessions); that's the provider's case to make with a modifier.
What to do next
- Contact the provider's billing office; they need to correct the coding or resubmit with the appropriate modifier and documentation.
- If the bill reaches you anyway, dispute it in writing citing the denial; a coding conflict between provider and insurer is theirs to resolve.
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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