CO-182: Procedure modifier was invalid on the date of service.
The modifier attached to the procedure was not a valid modifier as of the date of service, similar to code 181 but for the modifier rather than the base code.
What the group code means
- CO
- Contractual Obligation. The provider is responsible and the amount cannot be billed to the patient.
Why it fires
- The modifier had been retired or had not yet been introduced as of the date of service
- The modifier was mistyped or transposed into an invalid value
Corrective actions, ranked
- 1
Check modifier effective dates
Confirm the modifier was active for that specific date of service.
- 2
Correct the modifier
Replace with the valid, equivalent modifier for that period and resubmit.
- 3
Update your coding reference tables
Refresh the modifier list your billing system uses each year.
Is it worth appealing
Not an appeal. Correct the modifier and resubmit rather than appealing.
Retrieved 2026-07-18.
Do not let this happen again
Scrub the claim against NCCI PTP and MUE edits before you submit, free and in your browser.
DenialPath provides billing and administrative guidance based on published CMS and X12 sources. It is not medical advice, not a coverage determination, and not a guarantee of payment. NCCI and MUE edits are republished quarterly and payer policies vary by contract. Always confirm against the payer's own current policy before submitting or appealing.