Kidney Disease - Long Term Complications: Diabetes

Content provided by the Faculty of the Harvard Medical School

Kidney disease

In the past, about 10%–35% of people with diabetes have developed kidney disease, or nephropathy. Kidney disease is progressive; the deterioration can eventually leave the kidneys unable to filter wastes from the body. This is known as kidney failure or end-stage renal failure. Although diabetes is the leading cause of kidney failure, accounting for about 40% of new cases, most people with diabetes don't develop this life-threatening condition.

In type 1 diabetes, the kidneys can suffer damage as early as within 5 years of diagnosis, although it usually takes 20 years before kidney failure occurs. Kidney disease is more common in type 1 than in type 2 diabetes. But hypertension, which is a problem for many with type 2 diabetes, can increase your chances of developing this condition and accelerates its progression.

What goes wrong?

Kidneys filter toxins and wastes from the bloodstream, flushing them out of the body through urine, while retaining important proteins and other useful substances. This filtering work is done by glomeruli, a delicate network of capillaries. But after prolonged exposure to high blood sugar, capillary membranes thicken, and the glomeruli are damaged and distorted.

One of the first signs of kidney disease is an elevation in the level of the protein albumin in the urine. Most healthy people excrete less than 30 mg of albumin, the most abundant protein in blood, in the course of a day. In the initial stage of diabetic kidney disease, called microalbuminuria, more albumin (30–300 mg) appears in the urine each day because of leakage through the damaged glomeruli.

Most people with microalbuminuria go on to develop full-blown kidney disease. The next phase, known as clinical albuminuria (in which up to several grams — the equivalent of thousands of milligrams — of albumin are excreted each day), may not occur for another 10–15 years. Over the next 5–10 years after the development of clinical albuminuria, more than 90% of those affected will undergo a steady loss of the filtering capacity of their kidneys.

Because healthy kidneys can function at about 10 times the capacity of what's needed for survival, symptoms don't occur until 90% of kidney function has been lost. The inability to eliminate excess water and salt produces or worsens hypertension. Your body starts to retain fluid, causing weight gain and the swelling of your hands and feet. Without an effective filtering system, toxins accumulate, causing symptoms such as nausea, fatigue, vomiting, loss of appetite, weakness, and itching. At this point, kidney disease threatens survival and requires extreme measures, such as dialysis or transplantation.

Detecting kidney disease

High albumin levels are often uncovered by a random or "spot" urine test done during a regular doctor's appointment. If the level of albumin in your urine is high, your doctor may suggest another random urine test or ask you to provide a 12- or 24-hour urine sample. This involves collecting all urine for the specified period of time in a jug.

Physicians may also measure creatinine levels in the urine sample and a blood sample. Creatinine is a waste product of muscle and, usually, your kidneys easily excrete it. However, as your kidneys lose their filtering ability, creatinine excretion falls, and blood levels rise from a normal range of 0.5–1.5 mg/dL to as high as 10–15 mg/dL. For this reason, the blood creatinine level is a useful gauge of kidney health. Your doctor may also test your blood for sodium, potassium, and other substances and check for anemia, which often accompanies kidney failure.

Treating and preventing kidney disease

Strict blood sugar control is imperative. Long-term follow-up of the Diabetes Control and Complications Trial found keeping blood sugar close to normal decreases the risk of developing microalbuminuria and clinical albuminuria by 59% and 84% respectively.

Blood pressure must also be carefully controlled. Blood pressure goals are more stringent for everyone with diabetes, even those who don't have high blood pressure. Worsening kidney function is associated with high blood pressure and vice versa. Keeping blood pressure tightly controlled can reduce the progression of kidney damage in people with type 1 and type 2 diabetes. Losing weight and reducing your salt intake can help. If medications are needed, most doctors prescribe ACE inhibitors or angiotensin blockers to control high blood pressure in people with diabetes. These drugs retard the progression of kidney disease and may be used even when blood pressure is normal. These or other blood pressure medicines may also be used to normalize blood pressure into acceptable ranges.

Many doctors recommend low-protein diets for patients whose kidneys are deteriorating. These measures can slow the advancement of kidney disease and the eventual need for dialysis or kidney transplant, but they don't stop the process entirely. Many patients inevitably progress to end-stage renal failure. Although this condition used to be fatal, now there are two treatment options: dialysis and kidney transplantation.

Dialysis. There are two types of dialysis: hemodialysis and peritoneal dialysis. In hemodialysis, blood is removed from an artery and sent through a machine that filters out wastes and toxins and returns the purified blood through a vein. Generally, hemodialysis is done at a hospital or clinic and involves three weekly treatments, each lasting three to four hours. Peritoneal dialysis, which can be performed at home, uses the abdominal cavity as the filtering basin. A special fluid is introduced into the belly through a tube or catheter, and it draws waste products from blood through the peritoneum (the abdominal membrane). The waste-containing fluid is then drained out and discarded. Although dialysis often makes people feel better, several complications frequently occur, including infections and catheter blockage. In addition, dialysis often accelerates vascular disease and bone loss.

Transplants. A kidney transplant may be more desirable, particularly for younger people, but the surgery hinges on the availability of donor organs. Some people spend two or more years, often on dialysis, waiting for a compatible kidney. However, having a living, related donor makes the wait much shorter. After receiving a new kidney, an individual must take powerful drugs, called immunosuppressants, to prevent his or her body from rejecting the transplanted organ. Over the long term, these drugs may make the individual more susceptible to infection and certain malignancies, and they carry other side effects, such as weight gain and bone loss.

Last updated:	January 23, 2007