Patient Stan Lee has PPO healthcare insurance. He goes to a preferred provider dermatologist for removal of a small skin lesion. The insurer has agreed to pay its preferred providers $90 for this service. (The dermatologist's full charge for the service is $120.) The insurer pays only $20 because the policy requires a $20 patient co-payment and a $100 annual deductible. Prior to this service, Stan Lee had paid $50 of the deductible. Why can the dermatologist not bill Mr. Lee $100?

What will be an ideal response?

The dermatologist has a contractual agreement with the PPO insurer to charge only $90 for the service. Since the insurer paid $20, the dermatologist can only bill the patient $70: the $20 co-payment and the $50 remaining of the patient's annual deductible amount.