I know from my physical examination that urine occult blood is weakly positive in December, what is going on? Urine occult blood for weak positive, is determined by computer with test paper, mainly to determine the urine hemoglobin, it is a chemical reaction, there are many cases can occur false positive, so you must go to the hospital with a microscopic examination to see if there are red blood cells, such as red blood cells in the urine more than 3 / per high magnification field, before the diagnosis of hematuria.