What CO-4 means
The procedure code is inconsistent with the modifier used, or a required modifier is missing. A coding correction that resolves quickly with the right modifier and documentation.
Common causes
- Required modifier missing
- Invalid or contradictory modifier applied
- Modifier not supported for that procedure code
How to appeal CO-4
Identify and apply the correct modifier supported by the documentation, then resubmit or appeal showing the modifier accurately reflects the service rendered.
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