CO-18Contractual ObligationDuplicate
CO-18 Denial Code: Exact duplicate claim/service
This claim or service is an exact duplicate of a claim already submitted and adjudicated.
Why CO-18 happens
- ●Claim resubmitted before the original finished processing
- ●Same CPT billed twice without an appropriate modifier (e.g., 76/77)
- ●Automatic rebill triggered by clearinghouse or PM system
How to fix a CO-18 denial
- 1
Check claim status on the original submission first
- 2
If services were genuinely separate, resubmit with the correct repeat modifier and documentation
- 3
If the original paid, adjust off the duplicate
How to prevent it
Work claim status via 276/277 or portal instead of blind rebilling; use repeat modifiers correctly.
Drowning in CO-18 denials?
OakClaim works every denial within 48 hours and builds prevention rules so they stop recurring.