CO-18 — Exact duplicate claim or service
Claim-adjustment reason code 18 · typically reported as CO-18 or OA-18
What it means
The payer believes this claim duplicates one already received — same patient, code, provider, and date of service.
Why DME claims hit it
- Rebilling while the original is still pending
- Monthly rental lines submitted twice after a clearinghouse retry
- Resupply billed by two team members for the same period
How to fix it
- Check claim status on the original before rebilling
- If it’s genuinely a different service (e.g., bilateral), add the distinguishing modifier and resubmit
Appeal posture
If the "duplicate" is actually distinct, resubmit with documentation/modifiers proving it.
Related denial codes
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