Diabetic Kidney Problems

Diabetes mellitus is the leading cause of kidney failure in the United States. Although the early stages of diabetic kidney disease, or diabetic nephropathy, are subtle and often go unnoticed, the disease can eventually result in end-stage renal disease (ESRD) requiring kidney transplantation or dialysis therapy. This potentially deadly complication of diabetes mellitus has grown to great public health significance, given the high cost of dialysis and the shortage of organ donations.

The U.S. Centers for Disease Control and Prevention (CDC) reported that 300,000 new cases of diabetic ESRD occurred in the United States in 2002. This absolute number continues to grow, although the proportion of diabetics who get ESRD seems to be declining. Still, ESRD treatment cost the United States Medicare system $25.2 billion in 2002. Diabetic nephropathy can occur with both type 1 and 2 diabetes mellitus, although it may occur earlier in life in type 1 diabetics, because their disease generally begins in childhood. Certain ethnic and racial groups are at greater risk for diabetic kidney disease, including African Americans and Mexican Americans. Differences in risk may be due to socioeconomic or genetic factors.

Diabetic nephropathy is considered one of the microvascular complications of diabetes mellitus, resulting from damage to small blood vessels including those in the kidneys. The high glucose levels of diabetes damage the blood vessels and kidney tissue itself, causing a gradual decline in kidney function. This microscopic damage can be seen by taking a biopsy of the kidney, although this invasive procedure is often not necessary for the diagnosis of diabetic nephropathy. The natural history of diabetic nephropathy is a gradual process that begins with albuminuria, a condition in which the kidneys leak more protein into the urine than normal, particularly the protein albumin. Normal urinary albumin excretion is less than 30 mg/day; albuminuria between 30 and 300 mg/day and greater than 300 mg/day is called microalbuminuria and macroalbuminuria (proteinuria), respectively. Microalbuminuria causes no symptoms and may already be present at the time that diabetes mellitus is diagnosed. Urinary albumin levels can be measured by using dipsticks tests on a single urine sample, by analyzing a patient's urine after a 24-hour collection period, or by testing the urinary ratio of albumin to creatinine, a waste product eliminated in the urine. With the worsening of kidney disease, microalbuminuria may progress to macroalbuminuria, which may in turn progress to an elevated creatinine level in the blood, representing the kidneys’ inability to adequately remove this waste.

To track the progression of diabetic nephropathy, nephrologists, physicians who specialize in the kidney, follow a patient's blood creatinine levels and glomerular filtration rate (GFR), a measure of the kidneys’ function. Kidney function may decline such that survival is not possible without kidney replacement therapy: dialysis or kidney transplant. About 2 percent of diabetics per year progress from macroalbuminuria to increased creatinine levels or ESRD. Once a person has macroalbuminuria, the median time to renal replacement therapy is 2.5 years.

The most effective way to prevent and treat diabetic nephropathy is through intensive glycemic control, measured by a patient's blood glucose levels and hemoglobin A1c (HbA1c) concentration. Treating high blood pressure in diabetics has also proven important to slow the progression of diabetic nephropathy, and the angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARB) are particularly effective drugs in decreasing diabetic albuminuria. Dietary protein restriction may also slow the progression of kidney disease. A patient who progresses to ESRD requires kidney transplantation or dialysis, a therapy whereby the patient's blood is cycled through a machine to remove the wastes normally filtered by the kidneys. Neither treatment is without its complications: kidney transplantation [Page 514]requires immunosuppressant drugs to prevent rejection of the new organ and dialysis is an invasive procedure often performed three times a week.

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