The Ohio Supreme Court has ruled that "both an original medical bill rendered and the amount accepted as full payment are admissible to prove the reasonableness and necessity of charges rendered for medical and hospital care."
The Court went on to say that "[t]he jury may decide that the reasonable value of medical care is the amount originally billed, the amount the medical provider accepted as payment, or some amount in between. Any difference between the original amount of a medical bill and the amount accepted as the bill’s full payment is not a “benefit” under the collateral-source rule because it is not a payment, but both the original bill and the amount accepted are evidence relevant to the reasonable value of medical expenses."
It should be noted that Ohio has a statute that modifies the traditional collateral source rule.
The case is Robinson v. Bates, 112 Ohio St.3d 17, 2006-Ohio-6362 (Dec. 20, 2006). Read the opinion here.