Proteinuria can be caused by diseases not involving the kidneys, such as multiple myeloma, a cancer of the plasma cells in the bone marrow. In this case, the blood is flooded with too many proteins that are then filtered into the urine. The condition is known as overflow proteinuria. The other type of proteinuria is due to kidney disease, such as glomerulonephritis, primary focal segmental glomerulosclerosis (FSGS) or kidney damage due to a systemic disease. Microalbuminuria means low levels of albumin are detected in the urine.