How does health insurance work in the US

In truth, health insurance works a little differently in each state
Rarely do they cover all the bills. Most often, patients pay a pre-negotiated portion - either a set dollar amount of a copay or a percentage.
4. In a perfect world, only doctors and their patients would have say over what treatments are performed. But, since this is by far NOT a perfect world, the insurance companies have the say. The patient doesn't get to choose the more expensive treatment - and the ONLY way it would be covered was if the patient and their doctor(s) can prove beyond a shadow of a doubt that by the insurance shelling out more money up front (in the form of the treatment) they would, in fact, save money in the long run - by not having to pay for complications or repeat proecdures.

If the patient ops to "top up" the treatment, they better have deep pockets because they'll probably end up paying for most, if not all of it.