EOB denial code CO-4: what it means

What it means

The insurer says the billing modifier attached to the procedure does not match the procedure code itself.

Contractual Obligation — an adjustment the provider agreed to by contract. The patient is generally not billed for CO amounts.

Official X12 description

“The procedure code is inconsistent with the modifier used”

Typical cause

A coding error on the provider's claim — a modifier that does not apply to the procedure, or a required modifier left off.

What to do next

1. 1This is generally a provider billing issue, not a patient-owed amount.
2. 2Contact your provider's billing office and ask them to review the modifier and resubmit a corrected claim.
3. 3Confirm with your insurer that you are not being held responsible for this line.