What does CO-18 mean?
CARC code 18 means the payer believes this claim is a duplicate of one already processed. First, verify whether you actually submitted this claim twice by checking your clearinghouse submission history. If it is a true duplicate, no action is needed. If the services were distinct encounters on the same date, resubmit using frequency code 7 (replacement) or 8 (void/resubmit) to indicate this is not a duplicate. Include documentation showing the services were separate and distinct. Overturn rate is approximately 70% when the claim is genuinely not a duplicate.
How to appeal CO-18
Check the RARC code
The RARC (Remittance Advice Remark Code) on your ERA provides specific details about why the claim was denied. This tells you exactly what needs to be fixed.
Correct the identified issue
Fix the specific billing or coding error identified. Verify the correction against payer guidelines before resubmitting.
Resubmit the corrected claim
Resubmit with the appropriate frequency code (7 for replacement, 8 for void/resubmit) along with the corrected information.
Key notes for behavioral health
Verify not a true duplicate. If distinct service, resubmit with corrected frequency code (7 or 8).