The effects of uncontrolled diabetes on the kidneys

Glomerulous Incoming arteriole Outgoing arteriole

Figure 5-3:

The kidney glomerular structure.

and its normal

Mesangium

Glomerulous Incoming arteriole Outgoing arteriole

Mesangium

Structure Kidney Glomerular

Kidney

Ureter

Bladder

Kidney

Ureter

Bladder

As diabetes proceeds, if control of the blood glucose is poor, the glomerular basement membrane and other nearby structures begin to thicken and take up the space occupied by the capillaries (see Figure 5-4). The tight quarters mean that the capillaries can't filter as much blood as they should. The rate of filtration, or glomerular filtration rate, begins to fall.

Figure 5-4:

The glomerulus in uncontrolled diabetes.

Figure 5-4:

The glomerulus in uncontrolled diabetes.

Structure Microalbuminuria

Microalbuminuria: An early indicator

As diabetes affects the kidneys, they begin to leak tiny amounts of protein. This indicator of kidney disease is called microalbuminuria and can be measured in a small sample of urine (see Chapter 7 for more about regularly testing for microalbuminuria).

Microalbuminuria should be measured on more than one occasion to confirm the elevation because many events can cause a falsely elevated reading, including the following:

t Blood in the urine t Fever tt Heavy exercise t Infection t Menstruation t Smoking t Very high blood glucose

Microalbuminuria is rare in children before puberty, regardless of the duration of the diabetes and the level of control. Some specialists suggest, therefore, that it isn't necessary to screen prepubescent children for microalbuminuria. The American Diabetes Association recommends that all patients with T1DM be screened for microalbuminuria beginning at five years after the diagnosis and every year thereafter.

Microalbumin can be detected about five years before a urine dipstick (which tests for macroalbuminuria — greater than 300 mg/ml) would test positive for albumin, which is great news because treatment in this early stage can reverse the kidney disease. A study in The New England Journal of Medicine in June 2003 showed that lowering blood pressure, blood glucose, and abnormal blood fats decreased the microalbuminuria and the decline in kidney failure.

Progressive changes

If the blood glucose isn't kept down so that a test called the hemoglobin A1c (see Chapter 7) is less than 7 percent over 10 to 20 years, changes begin to occur in the kidneys. The earliest signs are enlarged kidneys that seem to be functioning abnormally well judging by how fast they clear wastes from the body. This over-functioning results from the large amount of glucose that the kidneys are filtering. The glucose draws a lot of water with it, causing an increase in the pressure in each glomerulus.

After about two years of poor glucose control, a biopsy of the kidney should indicate that the basement membrane and the mesangium are thickened.

The next 10 to 15 years is a silent period during which there are no clinical signs that the kidneys are failing. But after 15 years of poor control, there are measurable signs of kidney failure as waste products accumulate in the blood, especially blood urea nitrogen and creatinine. This is the stage of azotemia, significant reduction in kidney filtration but not complete cessation.

By 20 years of poor control, the patient either begins dialysis or has a kidney transplant in order to survive. At this stage, the patient has uremia, which is an inability to cleanse the blood at all.

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