Anemia refers to a condition in which the red blood cell count, hemoglobin content, and hematocrit in a certain volume of circulating blood are all lower than normal standards. Among them, hemoglobin is the most important. If it is lower than 120g/L (12.0g/dl) in adult males and lower than 110g/L (11.0/dl) in adult females, it is generally considered anemia. Anemia is one of the most common clinical manifestations, but it is not an independent disease. It may be an important clinical manifestation of a basic or sometimes more complex disease. Once anemia is found, its cause must be identified. Anemia caused by different reasons includes iron deficiency anemia, hemolytic anemia, megaloblastic anemia, aplastic anemia, thalassemia, sickle cell anemia, congenital dyserythropoietic anemia, sideroblastic anemia, and myelophthisis anemia. Acute and chronic anemia: anemia caused by acute blood loss, chronic anemia (such as rheumatic anemia, anemia caused by infectious diseases, anemia caused by hypothyroidism, anemia caused by liver disease, chronic renal anemia, anemia caused by malignant tumors, etc.).