Denial codes / CO-18

Denial code 18

CO-18: Duplicate claim

Exact duplicate claim or service.

What to doRead the EOB, then decide
Often recoverableUsually not

The letters in front matter. CO means the office can't bill the patient for the amount; PR means the patient may owe it. The same number can appear with either, so read both parts.

Why dental offices see it

  • The claim was resent while the original was still processing.
  • The same procedure was entered twice in the practice software.
  • A corrected claim was sent as a new claim.

What to do

  1. Find the original claim and check whether it was paid, pending or denied.
  2. If paid, close the duplicate. If pending, wait or call. If denied, work the original denial.
  3. If the services were genuinely separate, appeal with notes showing two services.

Stop it next time

Check claim status before resending, and send corrections as corrected claims.

How many CO-18 claims are in your report? The free check counts them, ranks them by dollars and deadline and drafts the letter. It runs in your browser; nothing is uploaded.

Run the free check

Plain-English paraphrase; the official code list is maintained by X12. Insurer rules vary; check the insurer's provider manual. Not legal advice.