Denial Code CO-18: Description, Meaning and How to Fix It
The payer received this exact claim/service already.
Official description
Exact duplicate claim/service.
Common cause
The claim was submitted twice, or a resubmission was read as a duplicate rather than a corrected claim.
How to fix it
Confirm the original claim's status. If a correction is needed, submit a corrected claim (frequency code 7), not a fresh duplicate.
Related denial codes
- CO-45: The amount billed is higher than the payer's contracted (allowed) rate. The difference is a contractual write-off, not a patient balance.
- CO-16: The claim is missing required information or has an error. It is almost always paired with a RARC that names the specific missing field.
- CO-97: This service is bundled into another service that was already paid, so it is not paid separately.
- CO-22: Another insurer should be billed first under coordination of benefits.
- CO-29: The claim was submitted after the payer's filing deadline.
- CO-50: The payer decided the service was not medically necessary as billed.