Hematuria (or blood in the urine) should be investigated, as someone has already commented. The most common
causes are urinary tract infection and
kidney stones. It is possible to have either one without symptoms. My guess, though, is that you don't have a urinary tract infection, because your doctor would have seen evidence of that on the urinarlysis as well (white blood cells, leukocyte esterase, nitrates, etc) and probably commented on it.