One unit of blood is about 120mL, and one unit of blood is separated from 200mL of blood as the red blood cell pressure area is 40%-50% under normal circumstances, which means that the volume of red blood cells is about 80-100mL after one unit of blood is separated. At the same time, other substances such as anticoagulants are added to the separated red blood cells, and the volume of a unit of blood is about 120mL. In clinical practice, red blood cells are given to patients on a per-unit basis. Generally, when one unit of red blood cells is transfused, the patient’s hemoglobin can be increased by about 3-5g. In this way, it is possible to deduce approximately how many units of red blood cells a patient needs to be transfused according to the patient’s anemia level, thus providing a certain basis for clinical blood transfusion.