CO-18 Denial Code: Exact duplicate claim/service
The payer thinks it already processed this claim. Sometimes true; frequently a resubmission you sent because the first one was stuck, or two distinct same-day services that look identical.
Why it happens
- Genuine duplicate submission (double data entry, auto-rebill)
- Resubmission of a claim the payer never adjudicated
- Two distinct same-day services with identical coding, missing the distinguishing modifier (76/77, RT/LT)
- Corrected claim submitted without the corrected-claim frequency code
How to fix it, step by step
- Locate the 'original' the payer matched against — was it actually paid? To whom?
- If the original is unpaid/stuck: call/appeal to force adjudication of the original
- If services were distinct: resubmit with the repeat/anatomic modifier and notes
- Always send corrected claims with frequency code 7, not as fresh claims
Is it worth working?
Moderate — the work is establishing which claim is real and forcing the payer to adjudicate it.
Moderate — the work is establishing which claim is real and forcing the payer to adjudicate it.
How much is your practice writing off to denials like this?
Send 6 months of remittance files (3 clicks in your billing software) — get a free one-page scorecard of your denied dollars, what's recoverable, and your top payer patterns — within one business day of receiving your files. Recovery is contingency-only: no fee unless money posts.
Get the free denial auditMore codes: the Claimmender denial-code library.