What causes protein in the urine?

A lot of causes. In young people protein in the urine is usually due to heavy exercise or could be due to standing too long but it usually is minimal. The most common pathological cause of protein in the urine is diabetes followed by hypertension. Other causes are usually "glomerulonephritis" which are a group of diseases affecting the functional units of the kidneys. If you have protein in the urine call ur doc.