Anemia is a clinical syndrome that occurs when the total number of red blood cells in the peripheral blood is lower than normal. In clinical practice, the severity of anemia is often indicated by the hemoglobin concentration. For adult men, a hemoglobin concentration of 90-120 g/L is mild anemia; a hemoglobin concentration of 60-90 g/L is moderate anemia; a hemoglobin concentration of 30-60 g/L is severe anemia; and a hemoglobin concentration of less than 30 g/L is very Severe anemia. For adult women, hemoglobin concentration between 90-110g/L is mild anemia; hemoglobin concentration between 60-90g/L is moderate anemia; hemoglobin concentration between 30-60g/L is severe anemia; and hemoglobin concentration below 30g/L is very severe anemia. Therefore, in clinical practice, the severity of anemia often determines the severity of the disease, especially in patients with severe anemia and very severe anemia, which often require timely hospitalization and even blood transfusion treatment.