Proteinuria, or excess protein in the urine, can be caused by many diseases and conditions. It can even be caused by side effects from a medication you might be taking. Diabetes is very common cause of proteinuria. If you have diabetes, controlling your blood glucose and modifying your medications can prevent or reduce proteinuria. If you have high blood pressure, your doctor may tell you to take a medicine to help lower your blood pressure and protect your kidneys from further damage.