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.
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