There are about three ways to classify anemia: first, according to the cell dosimetry classification, it is divided into macrocytic anemia, normocytic anemia, and small cell hypochromic anemia. In macrocytic anemia, the average red blood cell volume is >100fl and hemoglobin is >32g/L, in normocytic anemia, the average red blood cell volume is between 80-100fl and the red blood cell hemoglobin content is 26-32g/L, and in small cell hypochromic anemia, the average red blood cell volume is <80fl and red blood cell hemoglobin is <26g/L. Second, according to the severity, the anemia is classified into mild, moderate, and severe and very severe anemia. Mild anemia, hemoglobin >90g/L, but lower than normal value. Moderate anemia, hemoglobin is between 60-89g/L. Severe anemia with hemoglobin between 30-59g/L. Very severe anemia, hemoglobin <30g/L. Third, according to the etiology and pathogenesis, there are erythropoiesis-decreasing anemia, erythrocyte destruction-increasing anemia, i.e. hemolytic anemia, and blood loss.