According to the World Health Organization, anemia is diagnosed based on the level of hemoglobin, which is the main component of red blood cells in routine blood tests. The normal range of hemoglobin is different for different ages and genders. Anemia is diagnosed in adult males with hemoglobin below 130g/L, in adult females with hemoglobin below 120g/L, in pregnant women with hemoglobin below 110g/L, in children younger than 6 years old with hemoglobin below 110g/L, and in children 6-14 years old with hemoglobin below 120g/L. Hemoglobin is composed of iron ions and pearl proteins, and the human body is rich in protein reserves but limited in iron content, so most of the problems of anemia appear in iron ions. If anemia is diagnosed, we need to check ferritin, serum free iron and transferrin saturation to exclude iron deficiency anemia.