Diabetic nephropathy is a type of kidney disease in which the kidneys can no longer function efficiently. Diabetes affects the kidneys by causing the blood vessels to become blocked and leaky. When the kidneys function properly, they filter out waste products from the blood.

The kidneys are bean-shaped structures located in the middle of the back on both sides of the spine. Although small, the kidneys receive about 20 percent of the blood pumped by the heart. In addition to removing waste, the kidneys:

• Maintain the water volume of the body
• Regulate blood pressure
• Maintain calcium level within the body

Each kidney is about the size of a fist and is composed of roughly 1 million filtering units called nephrons. The nephrons themselves are made up of blood vessels called glomeruli.

The glomeruli filter out molecules of waste products and water through constant, stable pressure but do not filter out red blood cells. The waste products form urine, which moves to the bladder to be eliminated while blood returns to the body.

When the nephrons become damaged, the glomeruli can leak protein into the urine, including a type of protein called albumin. This protein helps fluid remain in the bloodstream instead of leaking into the tissues. Diabetic nephropathy can cause the kidneys to lose large amounts of albumin, leading to a condition called microalbuminuria. As a result, the body retains a large amount of waste products and loses important nutrients.

A microalbuminuria test, a special type of urine test, can detect kidney damage early. If microalbuminuria is not found and treated, the result is further kidney damage and the loss of larger amounts of protein in the urine (proteinuria). Another useful tool for detecting and monitoring kidney damage is a calculation called glomerular filtration rate.

About 10 to 20 percent of people with diabetes have nephropathy, and about 40 percent of those with type 2 diabetes will eventually develop it, according to the American Diabetes Association (ADA). Severe nephropathy is more common with type 1 diabetes. Twenty to 40 percent of people with type 1 diabetes experience kidney failure by age 50, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Patients with nephropathy often have the eye disease known as diabetic retinopathy as well. Both conditions are forms of diabetic angiopathy (blood vessel disease). In addition, proteinuria, a hallmark of diabetic nephropathy, has also been linked to heart disease in people with type 2 diabetes.

The ADA estimates that, compared to whites, nephropathy is 2.6 to 5.6 times more common in non-Hispanic blacks, 4.5 to 6.6 times more common in Mexican Americans and 6 times more common in American Indians.

Recent research reveals that people with prediabetes can develop diabetic complications including nephropathy, retinopathy, neuropathy (nerve disease) and heart conditions. In a seven-year project, scientists from the National Institutes of Health (NIH) and elsewhere found that people with prediabetes developed more chronic kidney disease than those with normal glucose (blood sugar) but less than those with diabetes.

End-stage renal disease (ESRD) is the point when the kidneys stop working. Dialysis or a kidney transplant is necessary for survival. About 44 percent of new cases of ESRD are due to diabetes, according to the NIDDK. However, nephropathy can be delayed or even prevented through glucose control, careful monitoring and treatment.

Several recent studies offer promising developments in diabetic nephropathy:

• Despite the increasing incidence of diabetes, the rate of kidney failure in diabetic Americans has dropped 30 percent since its peak in 1996, the Centers for Disease Control and Prevention (CDC) reported in 2005. The CDC also estimated that hospitalization rates for diabetic complications such as kidney failure declined 35 percent between 1994 and 2002.
  
  
• U.S. rates of kidney failure have stabilized since 1999 after a two-decade surge in which rates increased 5 to 10 percent a year, the NIDDK reported.
  
  
• The incidence of ESRD in people with type 1 diabetes appears to have fallen. In a decades-long nationwide study in Finland of 20,000 young people with type 1 diabetes, 2.2 percent of the patients had ESRD 20 years after diagnosis and 7.8 percent after 30 years. This rate is markedly lower than (older) U.S. estimates by the NIDDK. The investigators attributed the improvement to advances in treatment.
  
  
• The long-term Pittsburgh Epidemiology of Diabetes Complications Study (EDC) in 2006 also found declining rates of kidney failure in people with type 1 diabetes. Eighteen percent of those diagnosed with diabetes in the 1960s had kidney failure 30 years later, compared to 31 percent of those diagnosed in the 1950s.