2. Kidney Disease
Another of the more worrying potential causes of blood in the urine is kidney disease. Here, microscopic urinary bleeding is caused by glomerulonephritis, which in turn is inflammation of the filtering system in the kidneys.
This can be a symptom of a systemic disease such as diabetes. In some other cases, it might occur on its own for no obvious reason, or it might be triggered by strep infections, blood vessel diseases (called vasculitis) or immune problems (like IgA nephropathy).
Kidney disease can cause a range of other problems so look out for more symptoms.