The majority of causes of blood in your urine are not dangerous, but red or white blood cells in your urine might indicate a medical problem that requires treatment, such as kidney illness, urinary tract infection, or liver disease. White blood cells (WBCs) in your urine may also be seen after exercise or sexual activity and usually goes away on its own within 24 hours. Kidney disease is one cause of blood in the urine. The kidneys filter out waste from the body through urine, so if they aren't working properly, you will start to build up this waste material in your blood and other parts of the body. This waste material can then end up being passed in your urine. Blood in the urine can also be caused by problems with the lining of the bladder or urinary tract. These problems include injury, inflammation, and cancer. In addition, women often experience blood in the urine after having a baby because the birth process can damage the bladder muscle layers causing leaks into the urine stream. As we age, our ability to empty our bladders decreases which can lead to repeated episodes of blood in the urine. Finally, blood in the urine can be a sign of an infection. A small amount of blood in the urine does not necessarily mean that you have an infection. However, if the blood is mixed with white cells, it is likely to be due to an infection.