CARC 18 — Duplicate Claim/Service

CARC 18 — "Exact duplicate claim/service"#

Official meaning: CARC 18 reads "Exact duplicate claim/service." The payer has determined the claim or service line duplicates one already received (and possibly already paid or in process).

What it means in practice: the same claim was submitted more than once for the same patient, provider, date of service, and procedure. Causes include resubmitting a claim while the original is still in process, billing systems sending duplicates, or staff resubmitting because they did not see the first claim's status.

Is it a real denial? Often it is a *false* duplicate. Two legitimately separate services can look like duplicates to the payer's edit — for example, the same procedure performed twice on the same day (bilateral, repeat lab draw, multiple units). In those cases the services were not duplicates at all.

How to resolve CARC 18:

1. Check claim status first (276/277). If the "original" is still processing, simply wait — do not resubmit, which only creates more duplicates.
2. If it is a true duplicate already paid, no action is needed; the duplicate is correctly denied.
3. If the services were genuinely distinct, resubmit with the appropriate modifier to show they were separate — e.g., modifier 76 (repeat procedure by same provider), 77 (repeat by different provider), 59/X{EPSU} (distinct procedural service), or anatomical modifiers — with documentation, or appeal with proof the services were not duplicates.

Prevention: automated claim-status checking (276/277) before resubmission, and submission controls that block accidental duplicate sends, prevent most CARC 18 denials. This is a classic example of a "process discipline" denial rather than a clinical or contractual one.