Final answer:
Diabetes (option a) is the leading cause of kidney failure in Americans over 20, due to the progressive kidney damage resulting from diabetic nephropathy, which damages the kidneys' filtering capillaries.
Step-by-step explanation:
The leading cause of kidney failure in Americans 20 years of age and older is diabetes. Diabetic nephropathy is a progressive kidney disease caused by damage to the capillaries in the kidneys because of long-standing diabetes mellitus. Over time, high levels of glucose in the blood damage the filtering capillaries, leading to kidney failure, where the kidneys can no longer adequately filter metabolic wastes from the blood.
Overall, diabetes mellitus is the most common cause of chronic kidney disease (CKD), particularly stage 5 CKD, which is a severe illness requiring dialysis or a kidney transplant. Other causes of kidney failure can include polycystic kidney disease (PKD) and chronic hypertension, but diabetes remains the primary culprit in America for kidney-related complications leading to renal failure.