Before the blood test, it is required that you should not eat for at least 6 hours, that is, if the blood is drawn at 6 o’clock on the morning of the second day, it is required that you should not eat or drink after 12 o’clock on the night before. For example, drinking water before the blood is drawn may cause the patient’s blood to be diluted, which can lead to a certain degree of decrease in white blood cell, red blood cell and platelet counts when performing routine blood tests. If starchy food is eaten before the blood is drawn, it may affect the blood glucose level because fasting blood glucose is usually required, and if it is eaten, the patient’s blood glucose may rise, possibly reaching about 8 mol/L or 9 mol/L.