Urine protein testing is used to detect protein in the urine (proteinuria). There are three main mechanisms to cause proteinuria: disease in the glomerulus; increased quantity of proteins in serum (overflow proteinuria); low reabsorption at proximal tubule (Fanconi syndrome). Proteinuria can also be caused by certain biological agents, such as bevacizumab (Avastin) used in cancer treatment, or by excessive fluid intake (drinking in excess of 4 litres of water per day). Proteinuria may be a sign of renal (kidney) damage.