Duplicate depends on the facts

Denial Code CARC 18: Exact duplicate claim or service

CARC 18 means: exact duplicate claim or service. Here's what it means in plain English, why it happens, and how it's worked toward payment.

CARC 18 — Exact duplicate claim or service. Denial family: Duplicate.

Why you get a CARC 18 denial

The same claim was submitted twice.
A legitimately repeated service wasn't flagged as distinct (missing 76/77 or anatomic modifier).
A resubmission crossed with the original in the payer's system.

How to fix or appeal CARC 18

Confirm whether it's a true duplicate or a distinct/repeat service.
If it's a genuine repeat service, resubmit with the correct repeat or anatomic modifier and documentation.
If it's a true duplicate already adjudicated, no resubmission — verify the original paid correctly.

Recoverable when it was actually a separate service mislabeled as a duplicate; otherwise it's a no-action confirmation.

Have a stack of CARC 18 (or other) denials piling up? Get a free forensic A/R audit →

CARC 18 — FAQ

Is a CARC 18 denial worth working?

Yes — many '18' denials are distinct or repeat services the payer's edit treated as duplicates. With the right modifier and documentation they're payable.

How do I prove a service isn't a duplicate?

Show it was a separate encounter or a clinically necessary repeat — date/time, distinct site, or a repeat-procedure modifier (76/77) supported by the record.