CARC 18
Exact duplicate
The payer has already received an identical claim and will not pay it twice.
Why you actually get this
- A claim was resubmitted before the original finished adjudicating.
- An automated resubmission fired on a claim already in process.
- A genuinely distinct second service was billed without a modifier distinguishing it.
How to check whether it’s correct
- 01Find the original claim and confirm its status before doing anything else.
- 02Establish whether the second service was genuinely distinct — same day, different site or session.
- 03Review whether automated resubmission rules are firing too early.
Sometimes worth appealing
If it is a true duplicate, there is nothing to recover and the original is probably paying. If the second service was genuinely distinct, the appeal needs a modifier and documentation establishing the distinction.
Often arrives with
Seeing a lot of these?
A single denial is a claim to work. A pattern of the same denial is a process to fix, and the two need completely different responses. A free panel reads ninety days of your claims data and shows which codes actually recur for you.
Claim Adjustment Reason Codes are maintained by X12 as External Code List 139. The official description of this code is theirs and is not reproduced here. Check the authoritative list for current wording and status.