Official CARC description: “Diagnosis was invalid for the date(s) of service reported.” Here’s what it actually means, why it fires, and how to get the claim paid.
The ICD-10 code wasn't valid ON THE DOS — deleted codes, codes not yet effective, or October 1 codeset-transition casualties.
Liability group: CO = Contractual Obligation — the provider absorbs it — the amount cannot be billed to the patient. If the denial is wrong, the money is recovered by correcting or appealing the claim, not by balance-billing.
Also written: CO-146, CO146, “denial code 146”, “146 denial code” or “reason code 146” — same CARC, different ERA formatting.
Validate the code's effective window against the DOS
Replace with the code valid on the DOS; corrected claim
Verify the DOS itself — sometimes the date is the error
Update EHR favorites/order sets every October 1
Not appealable — codeset validity is mechanical. The win is preventing it: codeset-update discipline each October.
Fill in the denial facts — use placeholders, never real patient data (the letter keeps [PATIENT NAME]-style fields so you can merge real details privately). A payer-ready draft with an enclosure checklist comes back in ~20 seconds.
Your appeal letter draft will appear here.
The official CARC description for CO 146 is: “Diagnosis was invalid for the date(s) of service reported.” In practice: The ICD-10 code wasn't valid ON THE DOS — deleted codes, codes not yet effective, or October 1 codeset-transition casualties.
Denial code 146 under the CO group (Contractual Obligation) means: Diagnosis was invalid for the date(s) of service reported. The number is the reason; the CO prefix decides who is liable — the provider absorbs it — the amount cannot be billed to the patient. If the denial is wrong, the money is recovered by correcting or appealing the claim, not by balance-billing.
Yes. CO 146, CO-146, CO146 and “denial code 146” are the same CARC — clearinghouses, payer portals and PM systems just print it differently. Only the group prefix (CO, PR, OA or PI) changes the meaning, because it changes who has to absorb the amount.
CO stands for Contractual Obligation — the provider absorbs it — the amount cannot be billed to the patient. If the denial is wrong, the money is recovered by correcting or appealing the claim, not by balance-billing.
Not appealable — codeset validity is mechanical. The win is preventing it: codeset-update discipline each October.