Kidneys can fail for many reasons. The most common causes are diabetes and high blood pressure, which together account for about two thirds of all cases. Other causes are chronic inflammation that causes progressive loss of nephrons, polycystic kidney disease (the accumulation of cysts in the kidneys), scarring from untreated kidney or urinary tract infections, and obstructed urine flow.
A person with diabetes has too much sugar in his or her blood. Over time, high blood sugar damages small blood vessels in the kidneys (and throughout the body). As a result, diabetes reduces kidney function. Likewise, high blood pressure also damages the kidneys’ blood vessels. Kidney damage, in turn, may cause the blood to retain excess fluid, driving blood pressure even higher and setting into motion a dangerous cycle.
One treatment option for kidney patients is dialysis. The dialysis machine pumps blood out of the patient’s body and past a semipermeable membrane. Wastes and toxins, along with water, diffuse across the membrane, but blood cells do not. The cleaned blood then circulates back to the patient’s body. The procedure requires hours a day, several times a week.
Dialysis membranes cannot replace all of the kidney’s functions. For example, nephrons selectively recycle useful components such as glucose and salts to the blood. The dialysis machine cannot do this, although a technician can adjust the concentrations of dissolved compounds removed from the blood.
Transplantation is a second option. The transplanted kidney may come from a cadaver, or a living person may donate one healthy kidney to a recipient. Surgeons connect the new kidney to the recipient’s blood supply and attach its ureter to the bladder, usually leaving the old kidneys in place.