835 Denial Combination
CO-18+MA61
Contractual Obligation · Claim + Service Level Adjustment
Duplicate ClaimWhat This Combination Means
This combination indicates the payer identified the claim as an exact duplicate of a previously processed claim, with the additional issue of a missing, incomplete, or invalid social security number. The duplicate nature is the primary reason for adjustment, while the SSN issue provides supplemental context that may have contributed to claim identification problems or may need correction before any resubmission attempt.
Financial Responsibility
provider writeoff
Provider must write off the adjusted amount under contractual obligation. Patient cannot be billed for duplicate claim adjustments.
N/A
Appeal Success
Immediate (write-off after verification)
Avg. Resolution
Easy
Difficulty
No
Appealable
Step-by-Step Resolution
Steps tailored specifically to this CO-18+MA61 combination — not generic advice.
- 1
Search claim history by patient name, date of service, and procedure codes
Locate the original paid claim to confirm this is truly a duplicate submission rather than a legitimate separate service
- 2
Compare social security numbers between original and duplicate claims
Determine if SSN discrepancy caused duplicate processing or if SSN was missing/invalid on both submissions
- 3
Write off the adjustment amount and update billing system
Post contractual adjustment, note duplicate status, and correct SSN in patient demographics to prevent future submission errors
Specialty Context
How CO-18+MA61 typically presents across different practice types.
Dental
Verify SSN matches subscriber information from eligibility verification; duplicate claims often occur when same-day procedures are split across multiple claim forms
Medical
Common in scenarios where claims are resubmitted due to perceived non-payment without checking remittance status; SSN errors may stem from registration issues at front desk
Behavioral Health
Frequent when ongoing therapy sessions are billed in batches and resubmitted due to tracking errors; ensure SSN matches insurance card and is consistently entered across all claims
Individual Code References
View the standalone definition for each code in this combination.
Medicare Contractor Guidance for CARC 18
FCSO + Noridian + uhc + aetna + bcbs_azYou will receive this reason code when more than one claim has been submitted for the same item or service(s) provided to the same beneficiary on the same date(s) of service. OA18 = Exact duplicate claim or service.
How to Prevent CARC 18 Denials
- ✓
Before resubmitting a claim, check claims status via the SPOT or the Part B interactive voice response (IVR) system.
- ✓
Ensure necessary appropriate modifiers are appended to claim lines, if applicable, and resubmit the claim.
- ✓
Append the applicable modifier(s) to the procedure code even if the diagnosis indicates the exact site of the procedure.
- ✓
Do not resubmit an entire claim when partial payment made; when appropriate, resubmit denied lines only.
- ✓
Do not refile a claim if the total approved amount has been applied to the patient's deductible.
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