@cat1203, thanks for your post.
There are areas where this doesn't apply, the most obvious and most preclusive is the inability to choose your doctors.
If a person's physician doesn't (isn't willing to) include a medical necessity indication on their requisition for coverage of bone markers, they aren't approved with original or advantage medicare plans.
There is an advantage to the insurer to include physicians in their plans. Delay is often denial. Preapproval can be defacto denial.