Healthcare Error Code
Healthcare Insurance / Medical Billing
Claim Adjustment Reason Codes (CARC)
CO-128 | Invalid billing modifier
Industry
Healthcare
Canonical
/healthcare/error-codes/co-128/
Last Updated
Feb 25, 2026
Summary
This code indicates that the modifier submitted is invalid or not allowed for the billed service.
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What This Code Means
CO-128 is applied when a modifier does not meet payer rules for the reported procedure. Modifiers provide context for how services are performed. Invalid modifiers prevent accurate adjudication. This is a data validation issue rather than a coverage determination.
Where Users Usually See This Code
- Remittance advice
- Claim rejection notices
- Claim detail reports
Why This Code Appears
- Modifier not applicable to procedure
- Incorrect modifier usage
- Payer-specific modifier restrictions
What Typically Happens Next
- Claim line is denied or adjusted
- Reprocessing may be required
- Payment is delayed
What This Code Is Not
- It is not a non-covered service decision
- It is not a duplicate claim
- It is not a contractual adjustment
Troubleshooting Checklist
- □ Review modifier applicability
- □ Confirm payer billing rules
- □ Monitor modifier usage patterns
Notes And Edge Cases
Modifier rules vary by payer and program. Updates to billing guidelines can affect validity.
Related Codes
8 links
- CO-4 CodeService inconsistent with modifier
- CO-125 CodeSubmission/billing error
- CO-62 CodeNot covered for place of service
- CO-54 CodeMultiple physicians not allowed
- CO-11 CodeDiagnosis inconsistent with procedure
- CO-65 CodeProcedure code invalid
- CO-133 CodeIncorrect provider type
- CO-61 CodeProcedure not covered for age
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