CO-146 fires when the diagnosis submitted was not a valid code on the date of service. Diagnosis code sets are revised annually, and codes are added, deleted and redefined at the boundary.
What CO-146 means
Two patterns produce this. A claim for a service before the annual update, submitted after it, carrying a code that did not yet exist; and a claim carrying a deleted code that the practice management system still offers. Services spanning the boundary are the hardest case, because the correct code depends on the date of each line rather than of the claim. The fix is a corrected claim with the code that was valid on the day.
Why CO-146 fires
- The code was added in a later annual update than the date of service.
- The code was deleted before the date of service and remains in the local code list.
- A claim spans an annual boundary and carries one code across both periods.
- The system's code list was not updated at the annual revision.
Is CO-146 worth appealing?
Sometimes worth appealing
How to resolve or appeal CO-146
- 1
Check validity for the service date
Not for today. A code valid now may not have been valid then, and the reverse.
- 2
Split claims that span the boundary
Each line takes the code valid on its own date of service.
CO-146 — frequently asked
Why does my system still offer a deleted code?
Is this appealable?
Reason-code meanings are paraphrased from the X12 Claim Adjustment Reason Code list for plain-language reference; they are not reproduced verbatim. This is general information, not legal, coding, or medical advice — always confirm against the payer's remittance and policy.
Turn this CO-146 denial into a signed appeal
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