Cerebrospinal fluid occult blood test

In a clean test tube, add 2 to 3 drops of 204.7 mmol / L (5%) benzidine acetic acid solution, then add 1 to 2 drops of glacial acetic acid, add 0.2 to 0.4 ml of cerebrospinal fluid, mix well, and add 881.8 mmol / L (3% ) 0.5 ml of hydrogen peroxide solution, if it turns blue, it is positive, indicating that there is subarachnoid hemorrhage or cerebral hemorrhage at least 2 hours ago; if it does not change color, it is negative.