Leucocytes test strip is able to detect and react with leucocytes esterase that found in the azurophilic granules of granulocytic leucocytes in neutrophil.  Thus reaction with the strip and azurophlic granules in neutrophil detects white blood cells either intact or lysed, but lysed white blood cell can not be detected by microscopic examination.  But on the other hand, when RBC is compared with leucocytes, leucocytes test strip tends to have higher potential of having false negative results due to some sources like bacteria or drugs.