The blood test requires fasting from 8:00 p.m. the day before the test, and fasting for 12 hours, i.e. no water for 12 hours before the test. Routine blood test is a test to check whether the number, shape and ratio of various blood cells are normal. If you drink a lot of water before the blood test, the blood will be diluted and the test results may be affected. If the patient’s hemoglobin value measured without drinking water is 120g/L, and measured again after drinking water, the hemoglobin may drop to about 110g/L, changing from normal to suspected mild anemia, which will cause some interference to the doctor’s clinical diagnosis. In addition, it should be noted before the blood test that strenuous exercise is not advisable, and if you have already exercised strenuously, you should rest for half an hour before the test.