On your explanation of benefits or remittance, CO-A1 means: a generic 'claim denied' code used when no specific reason code fits; the real reason lives in the remark (RARC) codes — demand the specific reason in writing.
Is there an overturn-rate benchmark for this code?
Honest answer: no. State external-review programs are limited by statute to clinical-necessity disputes, so administrative and financial denial codes like this one never reach external review and no published overturn rate exists. Anyone quoting one for this code is inventing it.
What to do next
This is usually a paperwork or billing-mechanics issue: it is often fixed by the provider correcting and resubmitting rather than by a patient appeal — call the billing office first and ask them to fix and resubmit.
Always request an itemized bill and keep everything in writing.
Now turn the number into a dispute. Knowing your percentile is step one; the letter that cites it, the visit-code check, and the deadlines are the rest. Medigami builds those from your actual bill — medigami.com