Every insurance company in the United States, along with Medicare and Medicaid,
already has a fixed amount that they will pay the caregiver for administration of TPA. I guarantee it, even without bothering to look up what TPA is. If the procedure is covered by insurance
at all, there's a pre-approved reimbursement amount for doing it.
Outside of an expensive, time-consuming, and almost always useless appeals process, that flat rate is all the doctors are going to get. They can take it or leave it.
There are medical codes for every imaginable procedure, and essentially every medical code has a fixed, preset amount that the insurance company will pay to have it performed.