What CO-18 means
The payer already received a claim for this service and is treating this one as a duplicate.
The CO group code means this amount is a contractual obligation: under most contracts you cannot bill it to the patient.
Common causes
- Claim resubmitted while the original was still processing
- Corrected claim sent without the correct frequency code
How to fix it
- Check the status of the original claim before resubmitting
- Send corrections as a corrected claim (frequency code 7) with the original claim number
Check the remark code (RARC) that came with the denial and the payer's own policy, since rules vary by payer and plan. This is a plain-English summary written by GetMax; the official code text is published by X12 at x12.org/codes.
Prevent it next time
Most denials are caused before the claim is sent. See 12 ways to reduce claim denials, or let our denial management team work them for you.