Anemia is graded as follows: 1. mild anemia: hemoglobin level <12g/dL in men and <11g/dL in women; 2. moderate anemia: refers to hemoglobin level between 6-9g/dL; 3. severe anemia: hemoglobin level <6g/dL; 4. very severe anemia: hemoglobin level <3g/dL. moderate to severe anemia indicates that the patient is seriously ill and needs early intervention Treatment is needed to find out the cause of anemia and to provide symptomatic supportive treatment with blood transfusion if necessary, especially for severe anemia to critical anemia. Patients with underlying diseases, such as coronary artery disease, are advised to maintain a hemoglobin level above 9 g/dL, otherwise it may cause myocardial ischemia and induce angina attacks. In addition, due to the degree of tolerance of the body to anemia and the urgency of the disease, neurological symptoms, such as dizziness, headache, insomnia, and even significant weakness, poor appetite, and liver damage, may occur when suffering from acute anemia. Clinicians should take into account the specific situation to determine the cause of anemia and the need for interventional treatment, because severe anemia can be life-threatening, so patients should seek medical attention early once they become significantly unwell, so that the doctor can determine the cause according to the situation and treat the original disease as well as symptomatic supportive treatment, which has a better impact on the patient's prognosis.