My 11 year old son observed blood in dribbles after urinating. The blood was observed on tissue paper while wiping. One time was bright red drop, then next time bright red stringy, fiber like, then another time dark, rust colored blood droplet, liquid, on the tissue. The urine test in the Dr office detected high white blood cell count but the culture found no blood in urine nor bacteria. What could be the cause of this and should there be further testing?