Anemia is a clinical syndrome that occurs when the volume of red blood cells in the peripheral blood is lower than normal. Clinically, it is often indicated by the hemoglobin concentration to indicate whether anemia is present, and also by the degree of decrease in hemoglobin concentration to classify the degree of anemia. Clinically, hemoglobin between 90-120 grams is mild anemia, between 60-90 grams is moderate anemia, between 30-60 grams is severe anemia, and below 30 grams is very severe anemia. Therefore, the lower the patient’s hemoglobin is, the more severe the anemia is, and the more serious the patient’s condition is. In clinical practice, severe anemia is also frequently seen in patients with aplastic anemia or acute leukemia. Their level of anemia often reaches above severe anemia and requires prompt treatment. Of course, other types of anemia, such as iron deficiency anemia and megaloblastic anemia, can also present with severe anemia, but it is less common.