A predetermination does not guarantee that payment will be paid in full. We too have Highmark PPO and I will outline our experience with payment below:
Laser treatment- $7700 for Dr. Charge, Insurance co. paid $2200. This is what they felt was reasonable and customary. Balance $5500 due to doctor since he's out of network.
Surgery- $45,700 doctor charge, Insurance paid $8,900, this is what they feel is reasonable and customary charge for this procedure. Balance $36,000(approx) to doctor since he's out of network.
Each and every time the hospital was covered 100%, as well as the anesthesia, less our deductible of course.
So even though your insurance pays 80/20 that is not 80% of the entire bill, that is 80% of what the insurance company feels is reasonable and customary. Reasonable and customary is an average cost for the same procedure that is done by multiple doctors across the US.