The amount of blood in the human body is proportional to its own weight. Under normal circumstances, the weight of its own blood accounts for about 7%-8% of its body weight, and the greater the weight, the higher the total amount of blood in the body, for example, an adult weighing about 70kg has a total internal blood volume of about 4500-4800ml. A person with a smaller body weight will have a correspondingly lower amount of blood in his or her body. Clinically, if there is a patient with anemia, there is no significant difference in the blood volume in his body, which is also 7%-8% of his body weight, but the number of red blood cells is significantly reduced, in that the number of red blood cells contained in each milliliter of blood is reduced. Although the blood volume is normal, the total number of red blood cells is reduced, resulting in a patient with reduced oxygen-carrying capacity and symptoms of anemia, manifested as pallor, dizziness, weakness, panic attacks after activity, chest tightness, etc.