Maintaining Your Health on Mackinac
Understanding Chronic Kidney Disease and Kidney Failure
By Yvan Silva, M.D.

The kidneys lie in the back of your upper abdomen. They are sophisticated filters. Each contains about one million nephrons, the filtration units that work to regulate concentrations of salts, water, and some substances in the bloodstream as well as to remove wastes and toxic substances from the body. The center of a nephron, the glomerulus, is made up of a small bundle of blood vessels that intertwine and exchange blood across their membranes to form fluid. The fluid empties into microscopic tubules that join to form an elaborate drainage system to transport this filtration product as urine. It moves from the kidneys to pass through tubes, the ureters, into the urinary bladder.

About one-fifth of the blood pumped out of the heart with each pulse stroke is received by the kidneys. Thus, about 20 gallons of blood are filtered every day; the turnover results in about half a gallon that is excreted as urine. The kidneys also have elaborate hormones; renin helps regulate blood pressure, calcitriol is important for calcium absorption in bones, and erythropoietin works to produce red cells. The excretory functions of the kidneys are vital to normal physiology. They remove urea, a waste product of protein breakdown. Creatinine is a waste product of muscle metabolism; excess amounts of calcium, phosphorus, and potassium need to be carefully controlled in the bloodstream and the entire fluid balance in the body is achieved by controlling maintenance of salt and water content. The entire scope of kidney function is versatile. People can live a normal life with one kidney, making donation of one kidney a significant, important option.

Dialysis and transplantation become relevant when kidney disease progresses to end-stage kidney failure. This life-threatening situation is preceded by chronic kidney disease, a decline of kidney function that can go unnoticed unless it is detected early enough to be treated. About 15 to 20 million Americans are estimated to have chronic disease, and a great number of them are unaware in the earlier stages; about one-half of them are diagnosed in late stages.

Because the kidneys have an abundance of capacity, about 75 percent of overall function can be lost before symptoms and signs become apparent. The damage that has occurred cannot be undone, and in many cases it may be difficult to prevent. Kidney damage does not necessarily result in decrease in urine production. In early stages urine production may increase because of inability of the kidney to concentrate urine.

Although aging affects the kidneys, severe loss of kidney function is not the norm. The leading cause of kidney failure is diabetes. Diabetic nephropathy is progressive damage of the small blood vessels supplying the nephrons. In the United States, about half of the people who require dialysis or transplantation have diabetes as the cause of their kidney failure. About 30 percent of diabetics with either insulin or noninsulin dependent diabetes may develop failure - the longer the diabetic state the more likely. The two most important factors to manage prevention or delay are proper control of blood sugar and control of hypertension that is also often present. Hypertension is the second most common cause, even in the absence of diabetes. There are other causes, congenital or inherited, inflammation, obstruction to urine flow from the kidneys, and narrowing of the arteries from arteriosclerosis. Some medications taken over the long-term or in high doses may cause eventual failure.

When about 75 to 80 percent of kidney function is lost, symptoms and signs can follow. Fluid build-up can result in puffiness around the eyes on awakening, and swelling of the feet and ankles. As toxins accumulate, symptoms of chronic illness such as fatigue, poor appetite, weight loss, and neuromuscular symptoms appear.

Screening tests are important, especially if there is high risk. Often abnormalities are found during regular health checkups. Diabetic testing for blood sugar is indicated. Kidney function can be assessed with blood testing for creatinine, blood urea nitrogen, urinalysis for abnormal blood cells and protein and, when necessary, further tests of kidneys by CT or MRI and tests of function by clearance studies become relevant.

The priorities of management are control of hypertension, control of blood glucose (sugar) levels, treatment of anemia, and lifestyle changes including a prescribed appropriate diet, weight and cholesterol control, and regular checkups. When failure enters

the end-stage, dialysis (via the bloodstream, hemodialysis) or (via the abdominal cavity, peritoneal dialysis) is usually the first treatment employed. About 300,000 Americans receive dialysis regularly, usually as a bridge until a suitable kidney donation becomes available.

As in all health maintenance options available, testing of kidney functions is an important consideration. The basic testing is usually part of regular health checkups. People older than 60 and all others who have risk factors for kidney disease should get special attention. These include people with diabetes, hypertension, a family history of kidney disease, certain chronic conditions like lupus, or people in racial minorities in the U.S. and those on long-term medications that may affect the kidney adversely, and also those with early signs of deterioration of kidney function.

Dr. Silva is a professor of surgery at Wayne State University and a resident of Woodbluff on Mackinac Island.