CO-4 | Service inconsistent with modifier
This code indicates that the reported service is inconsistent with the modifier submitted on the claim line.
What This Code Means
CO-4 is used when a payer determines that a procedure or service does not logically align with the modifier attached to it. Modifiers provide additional context about how or why a service was performed, and payers rely on them to adjudicate claims accurately. When the modifier conflicts with the service description or payer rules, processing cannot proceed as billed. This does not automatically mean the service was invalid or unnecessary. It reflects a mismatch between reported information rather than a coverage decision.
Where Users Usually See This Code
- Electronic remittance advice (ERA)
- Provider claim rejection reports
- Claim detail views in payer portals
Why This Code Appears
- An incorrect modifier was appended to the service
- The modifier is not applicable to the reported procedure
- Payer-specific modifier rules were not met
What Typically Happens Next
- The claim line is denied or rejected
- Reprocessing may be possible with corrected information
- Payment is delayed until alignment is resolved
What This Code Is Not
- It is not a non-covered service determination
- It is not a contractual adjustment
- It is not an assessment of medical necessity
Troubleshooting Checklist
- □ Review payer modifier guidelines
- □ Confirm modifier applicability for the service
- □ Check payer-specific billing rules
Notes And Edge Cases
Modifier requirements vary significantly between payers. Some systems apply automated logic checks that flag inconsistencies immediately. Certain modifiers are valid only under specific clinical or billing scenarios.
Related Codes
- CO-16 CodeClaim lacks required information
- CO-125 CodeSubmission/billing error
- N20 CodeService not payable
- CO-11 CodeDiagnosis inconsistent with procedure
- CO-62 CodeNot covered for place of service
- CO-133 CodeIncorrect provider type
- CO-18 CodeDuplicate claim/service
- CO-65 CodeProcedure code invalid