Proteinuria means the appearance of protein in the urine. It is usually detected by a simple dipstick test of the urine. In some circumstances it is detected on a routine check. Usually there are no symptoms from it. Protein should not normally appear in the urine in detectable quantities.
Proteinuria is an indicator that the kidneys are damaged in some way.
Diseases that affect the filtering units themselves are the most common cause of heavy proteinuria. Sometimes this is called glomerulonephritis, meaning inflammation of the glomeruli. Just as some examples, any of the causes of nephrotic syndrome could be causes of proteinuria. A dipstick test of the urine detects albumin, which is an important protein component of the blood. Even small amounts of protein may be detected on dipstick testing.