Many patients see their urologist because they have either seen blood in their urine or have been told they have microscopic levels of blood in the urine when tested by their local doctor. It is never normal to have any blood cells in the urine but of course it is extremely common and in most cases there is no treatable cause identified. Whether you see the blood or not, or whether there is only one episode or more, blood in the urine always needs to be further investigated with some simple tests to be sure that there is no sinister underlying cause. Many patients feel that they may only have seen blood once and as it does not happen again they feel whatever the cause they are no longer at risk. This is definitely not the case as a bladder cancer, for example, may bleed once but may not bleed again for some time and if the diagnosis is missed, the cancer will obviously grow and potentially be more difficult to treat in the future.
Depending on your age, even microscopic blood in the urine can indicate the presence of an underlying cancer in the bladder or the kidney and again simple tests will help to determine if this is the case. Cancer is obviously in no way the most common underlying problem and in men bleeding is often related to kidney stones or an enlarged prostate and in women it is often related to infection or stones as well. Many cases of microscopic bleeding are related to a simple leakage of red blood cells through the filters in the kidney that therefore appear in the urine.
It is always prudent to seek specialist advice if blood is found in your urine and in most cases there would probably not be a significant underlying cause.