What color is it? Bright red or darker red? Bright red is fresh blood. Are you dehydreated? Have you been drinking? Is anything out of the ordinary? Does it hurt when you pee? Usually it means that you could have an infection, such as a kidney.. and I would get to your doctor for a check if you continue to pass blood more than once. Was it alot of blood or just a little bit. If it was just a little I would just watch it and if nothing more came out let it goe. If you continue to pass blood and it's bright red, get into the doctor and get it checked because you need some answers.