Question

main reason for kidney failure

Answer 1

In most cases the old kidneys will not be removed. this is because even failued kidneys release chemical that help the body work. However if those kidneys have a disease that cause on going problems such as persistent kidney infections or intestinal blockage,then the transplanting would be consideredremoving the old kidney.
The two most common medical conditions requiring "native nephrectomy" or "congential reflux" disease and polycystic disease