Denial Code CARC 18: Duplicate Claim or Service

CARC 18 means the payer flagged the claim as a duplicate. It is worth reviewing rather than writing off, because true distinct services, staged procedures, and bilateral or multiple-visit work are frequently misflagged as duplicates when the claim lacks the modifiers or documentation that distinguish them.

What this denial means

The payer’s system matched this claim to one it already has on file for the same member, provider, date, and service, and treated it as a repeat submission.

Why it happens

Sometimes it genuinely is a resubmission. Often it is not: a distinct service on the same day, a staged or bilateral procedure, or a second visit that was not distinguished with the correct modifier or a clear note. Resubmitting the same claim after a bounce also lands here.

The appeal angle that works

If the service was genuinely distinct, resubmit with the modifier that establishes it as separate (for example a distinct-service modifier) and documentation showing the two are not the same event. If it truly was a duplicate, there is nothing to recover, so the value of this code is knowing which is which quickly instead of forfeiting a real claim that was misflagged.

Questions

My claim was denied as a duplicate but the services were different. What now?

Resubmit with the modifier that establishes the service as distinct and attach documentation showing the two are separate events. Distinct same-day services, staged procedures, and bilateral work are commonly misflagged as duplicates when the distinguishing modifier is missing.