Helping Diabetic Kidneys Succeed Rather Than Fail

By Robert C. Stanton, M.D.
Chief, Nephrology Section, Joslin Clinic

Diabetes, particularly type 2 diabetes, has become so common that diabetic kidney disease (nephropathy) has leaped ahead of high blood pressure as the leading cause of kidney failure in much of the world. Kidney failure is a serious matter: The kidneys’ job is to filter waste products and excess fluids from the blood circulating through our bodies. If the kidneys fail, survival depends on either dialysis (being hooked up to a machine to do the kidneys’ blood-filtering) or a kidney transplant.

High blood glucose levels can damage blood vessels all over the body, including the tiny blood vessels that do the kidneys’ filtering. When those tiny vessels are damaged, they can’t do the job correctly. High blood pressure can result and make the problem worse, damaging more blood vessels and speeding up the progression of kidney disease. Both kidneys are affected. Though 20-40 percent of those with diabetes develop kidney disease, it can be slowed significantly if diagnosed early and treated.

Five principles should be followed by everyone with diabetes to help prevent and treat kidney problems:

• Tight control of blood glucose levels (A1C less than 7 percent)
• Tight control of blood pressure: aim for lower than 130/80
• Control of lipids: LDL (“bad”) cholesterol should be less than 100 mg/dl, HDL (“good”) cholesterol should be above 50 mg/dl and triglycerides should be less than 150 mg/dl
• No cigarette smoking
• Blood pressure-lowering drugs, such as ACE inhibitors or angiotensin receptor blockers (ARBs), are effective in protecting the kidney from damage if you have signs of diabetic kidney disease

The Earlier You Know, the Better

There are no symptoms in the early stages of diabetic kidney disease. Symptoms of kidney failure—fatigue, nausea and fluid retention—usually don’t occur until the late stages of kidney disease because the kidney can still adequately filter the blood even after extensive damage. Usually the first sign that the kidneys’ filtration system is damaged is an excess amount of protein in the urine, known as microalbuminuria. This is not just an early sign of kidney disease, but a well-established risk factor for cardiovascular disease, such as heart attack and stroke.

Two tests—one using urine and the other blood—must be performed annually for early detection. The urine sample is used to screen for microalbuminuria. The standard urine dipstick used in doctors’ offices does not measure this—a special machine is required instead. The blood sample is used to measure the level of creatinine, a substance normally present in the blood, which increases if your kidneys are not functioning properly. The blood sample results are then plugged into a formula that estimates your kidneys’ filtering capacity. The most commonly used formula is called the MDRD equation.

One cannot overemphasize how important it is to measure your blood creatinine and to use the MDRD equation to estimate total kidney filtering. The creatinine value alone can be misleading, as it must be interpreted within the context of age and gender. Patients often have more advanced kidney disease than their blood creatinine value alone suggests. For this reason, the National Kidney Foundation strongly urges all physicians to use the MDRD equation; however, not all (besides kidney specialists) routinely use it. An accurate estimate of your kidney function is essential for your doctor to decide what, if anything, needs to be done.

With aggressive treatment and yearly testing, we can greatly slow the decline in kidney function and reduce the number of people developing kidney failure.

This article appeared in the Special Diabetes Insert in the  November 21, 2005 issue of TIME Magazine.