Hello, and I hope I can help you today. The number of white and red blood cells in your urine has nothing to do with an STD or pregnancy. Urinary tract infections typically cause bacteria, a substance called leukocyte esterase, and nitrites to be present in your urine. Red blood cells can also appear if the inside of your bladder is inflamed from the infection. However, the presence of red blood in your urine can also be caused by other conditions of the kidneys or bladder that cause bleeding without infection. The most common of these is a kidney stone, and if you have had very severe pain in your back or lower pelvis, especially on one side, that diagnosis is also possible. Pregnancy or STDs do not generally cause blood to be seen in the urine. If you are concerned about pregnancy or STD exposure, these can be tested separately, but you do not have to be concerned about these conditions because of the presence of blood cells in your urine. I hope I was able to answer your question today and that my advice was helpful. Best wishes, Dr. Brown