China’s blood donation law stipulates that healthy citizens are advocated to donate blood without compensation, and it also stipulates that the interval between blood donations by healthy citizens should not be less than six months. That is to say, it is possible to donate blood again in about half a year, because when donating blood, the human body will lose 300-400 ml of blood, which includes all kinds of blood cells, such as red blood cells, white blood cells, platelets, and at the same time, it will also lose part of the plasma, which includes water, albumin, globulin, coagulation factors, inorganic ions, and so on. Normal bone marrow has a very strong compensatory function, which can make up the lost blood as fast as possible as soon as possible. However, the time for various cells to return to pre-donation levels varies significantly. For example, white blood cells can be restored to the pre-donation level in about 48 hours; platelets can be restored to the pre-donation level in about a week; and red blood cells usually take about 3-4 months to be restored to the pre-donation level. Therefore, in order to ensure the quality of blood and the health of the donors, China’s blood donation law stipulates that the interval between blood donations should not be shorter than 6 months.