The upper limit of blood sampling for adults is usually 400 ml. If too much blood is sampled at one time, it can lead to anemia and shock in patients. 1. The normal blood volume of the human body is around 4000~5000 milliliters. If you are drawing blood, you can’t draw any more if you draw up to 400 milliliters of blood. 2. A normal adult can only draw up to 400 milliliters of blood. If the body loses more than 800 milliliters of blood rapidly, there will be accelerated heart rate, anemia and hemorrhagic shock. If blood loss reaches 1200 mlll or more, it may be dangerous. Newborns, children, blood loss greater than 400 milliliters will cause sudden death. 3. Therefore, the national regulations stipulate that the maximum amount of blood to be drawn from an adult donor is 400 milliliters, which is within the safe range. If there is a situation where the patient loses too much blood, it is necessary to actively conduct blood transfusion to replenish blood volume.