Harvard Men's Health Watch

On call: Protein in the urine

Q. In the past you have discussed blood in the urine. I don't have that problem, but during my annual checkup last week, my doctor found protein in my urine. Is it a serious problem? And what should I do about it?

A. 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.

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