In general, the weight of blood in a person’s body is proportional to his or her body weight, and the weight of blood accounts for 7-8% of his or her body weight; the heavier the person is, the more blood there is in the body; the lighter the person is, the less blood there is in the body. A person weighing about 70 kilograms has about 4,500 milliliters of blood in his body, which translates into a kilogram weight of about 4.5 kilograms, and the blood in the body is closely related to his weight. Because of this, when donating blood in a clinical setting, the donor’s weight should be taken into account. For example, China’s blood donation law stipulates that a healthy adult male can’t weigh less than 50 kilograms when donating blood, and a normal adult female, can’t weigh less than 45 kilograms when donating blood. If the body weight is too light, the blood weight of the body will be less, and it will be easy to develop anemia, fatigue and other uncomfortable symptoms after blood donation.