Duplicate Claim Denials
CARC 18The payer already processed the same claim and won't pay it twice.
What it is
The pattern
A duplicate denial means the payer has already adjudicated the same claim — same patient, same service, same date — and will not process another. Legitimate corrections need a corrected-claim (frequency code 7) workflow, not a new claim.
Why it happens
Common causes
- The original claim was resubmitted because 'it wasn't paid yet' — creating a duplicate.
- A corrected claim was filed as a new claim, restarting adjudication and confusing the history.
- The same service was billed on two claim lines or two claims by accident.
Prevention
Stop it before the claim goes out
- Check claim history before resubmitting anything — the original may still be in process.
- Use frequency code 7 for corrections; never re-bill the same service as a new claim.
- Train staff on the difference between 'not paid yet' and 'denied'.
When it happens
What to do
If the duplicate is a mistaken re-bill, let the original claim stand or retract the duplicate. If the original was denied and the correction is legitimate, resubmit as a corrected claim — and if the payer treats a correction as a duplicate anyway, appeal citing the original claim number and the change you made.
Deeper dive
The full denial guide
The payer identified the claim as a duplicate of a previously processed claim. Verify the original before doing anything — this is often a no-action item.
Open the Duplicate Claims guide →