Healthcare Error Code
Healthcare Insurance / Medical Billing
Claim Adjustment Reason Codes (CARC)
CO-18 | Duplicate claim/service
Industry
Healthcare
Canonical
/healthcare/error-codes/co-18/
Last Updated
Feb 25, 2026
Summary
This code indicates that the claim or service has already been submitted and processed.
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What This Code Means
CO-18 is applied when a payer identifies a duplicate submission for the same service. The system detects matching claim details such as date, procedure, and provider. This prevents duplicate payment. It does not imply wrongdoing or error beyond duplication. The original claim typically determines final payment.
Where Users Usually See This Code
- Remittance advice
- Claim status reports
- Duplicate claim notifications
Why This Code Appears
- The same claim submitted multiple times
- Resubmission without required indicators
- System resends due to transmission issues
What Typically Happens Next
- The duplicate claim is denied
- The original claim remains valid
- No additional payment is issued
What This Code Is Not
- It is not a coverage denial
- It is not a billing quality issue
- It is not fraud
Troubleshooting Checklist
- □ Verify original claim status
- □ Confirm resubmission requirements
- □ Monitor duplicate prevention processes
Notes And Edge Cases
Some resubmissions are allowed with corrected information. Timing overlaps can create temporary duplicates.
Related Codes
8 links
- CO-98 CodeCharges already adjudicated
- CO-23 CodeImpact of prior payer adjudication
- CO-133 CodeIncorrect provider type
- CO-62 CodeNot covered for place of service
- CO-109 CodeClaim not covered by this payer
- CO-54 CodeMultiple physicians not allowed
- CO-61 CodeProcedure not covered for age
- CO-65 CodeProcedure code invalid
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