disease, tumours, pyelonephritis, exposure to nephrotoxins, and treatment with anticoagulants. Non-pathological hematuria can be observed after strenuous exercise and during menstruation. The normal number of red blood cells in urine should not usually exceed 3 per high power field. A urine test strip showing positive for blood can also indicate hemoglobinuria, which is not detectable using a microscope due to the lysis of red blood cells in the urinary tract (particularly in alkaline or dilute urine), or intravascular hemolysis. Under normal conditions the formation of haptoglobin-hemoglobin complexes prevents glomerular filtration, but if the hemolysis is extensive haptoglobin's uptake capacity is exceeded and hemoglobin can appear in urine. Hemoglobinuria can be caused by hemolytic anaemia, blood transfusions, extensive burns, the bite of the recluse spider (Loxosceles), infections and strenuous exercise. The urine test strip test for blood is based on hemoglobin's pseudo peroxidase activity in catalysing a reaction between hydrogen peroxide and the chromogen tetramethylbenzidine in order to produce a dark blue oxidation product. the resultant colour can vary between green and dark blue depending on the amount of hemoglobin. Catalysed by hemoglobin acting as a peroxidase H2O2 + Chromogen → Oxidised chromogen (coloured) + H2OThe reaction is not only catalysed by blood hemoglobin, other globins with a hem group such as myoglobin can also catalyse the same reaction. The presence of myoglobin in urine gives a positive reaction in the test strip's blood test but the urine appears clear with a red to brown colouration. The presence of myoglobin in place of hemoglobin can be caused by pathologies associated with muscular damage (rhabdomyolysis), such as trauma, crush syndrome, prolonged coma, convulsions, progressive muscular atrophy, alcoholism, heroin abuse and strenuous physical activity. The haem fraction of these proteins is toxic for the kidney tubules and elevated concentrations can cause acute kidney injury. It is possible to use an ammonia sulphate precipitation test in order to distinguish between hemoglobinuria and myoglobinuria. This consists of adding 2.8gr of ammonia sulphate to 5 mL of centrifuged urine, mixing well and after 5 minutes filtering the sample and centrifuging again. The hemoglobin precipitates out with the ammonia sulphate but not the myoglobin. Analysis of the supernatant for blood with a test strip will give a positive if myoglobin is present and a negative if hemoglobin is present. The test can give false positives if strong oxidant or peroxide residues are present on the laboratory material