Any degree of blood in the urine should be fully evaluated by a physician, even if it resolves spontaneously. Infection of the urine, (often called a urinary tract infection or UTI) stemming either from the kidneys or bladder, is a common cause of microscopic hematuria.Urine is naturally sterile and should not contain bacteria.ny degree of blood in the urine should be fully evaluated by a physician, even if it resolves spontaneously. Infection of the urine, (often called a urinary tract infection or UTI) stemming either from the kidneys or bladder, is a common cause of microscopic hematuria.