According to the hemoglobin concentration, anemia is classified as mild, moderate, severe and very severe. The specific grading criteria are as follows. I. Mild anemia, with hemoglobin concentration below the lower limit of normal, greater than 9 g/L, is manifested by patients who may experience mild weakness and dizziness, and some patients who are more tolerant may be asymptomatic and found only during physical examination. Second, moderate anemia, hemoglobin concentration between 6-9g/L, manifested as patients may show symptoms of anemia during activity. III. Severe anemia, with hemoglobin concentration between 3-6 g/L, manifests as the patient may experience weakness, panic, chest suffocation, and tightness of breath at rest, that is, in the resting state. Fourth, very severe anemia, with hemoglobin concentration below 3g/L, manifests as coma and drowsiness, with a very high risk of life.