Can highly recommend a nephrologist at Bumrungrad.
While fees for standard tests are fixed, his fees are very moderate. He will not sell you anything not needed. He listens to the patient & he asks questions. Not common with Thai doctors.
Was recently looking at renting an apartment/condo in Bkk. Very few landlords give you the actual bill. They charge you 8 Bht+++ per unit. No reduction gets passed on.
Their driving style also causes issues when they visit Europe e.g. stopping in the middle of a mountain pass for a photo or going down wrong direction in a oneway street.