Your kidneys have many functions, ranging from helping to regulate your blood pressure and stimulating the production of red blood cells to converting vitamin D into its active form. But their best-known job is to rid your body of excess fluids and metabolic waste products. To do that, the blood that flows into each kidney passes through about one million tiny vascular filters called glomeruli.
Healthy glomeruli allow water to pass into the urine, but hold back large molecules, such as the blood protein albumin. When glomeruli are damaged, though, they allow albumin to leak into the urine; albumin in the urine is called proteinuria.
Large amounts of albumin can be detected with a simple dipstick test, but a special chemical analysis is needed to detect small amounts (microalbuminuria). Until recently, doctors relied on 24-hour urine collections to evaluate proteinuria. Now, they can use a simple spot urine sample to measure the amounts of albumin and creatinine, another chemical that’s filtered from the blood into the urine. An albumin-to-creatinine ratio above 30 is abnormal; two or more abnormal results spaced over a three-month period indicate kidney disease and call for further evaluation.
Protein in the urine is an important indicator of kidney disease; microalbuminuria, for example, is often the first clue to diabetic kidney damage. And new evidence suggests that protein in the urine, even if it’s just early microalbuminuria, is an important harbinger of future heart disease; the more protein in the urine, the greater the risk. People with microalbuminuria are also at increased risk for high blood pressure and blood clots in veins.
When you get a report of an unexpected or abnormal lab result, the first thing to do is have the test repeated. If you do have proteinuria, a full evaluation of your kidney function is in order. You should also be sure to have your blood pressure, blood sugar, and cholesterol levels evaluated and, if abnormalities are found, treated. Blood pressure control is a particularly important way to protect your kidneys. Even if your blood pressure is OK, certain antihypertensive drugs (ACE inhibitors, angiotensin-receptor blockers, and certain calcium-channel blockers) can help preserve kidney function in people with proteinuria.
Your proteinuria may not turn out to be an important issue, but it does call for further evaluation and, perhaps, action.
– Harvey B. Simon, M.D., Editor, Harvard Men’s Health Watch
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