Iron deficiency anemia refers to the anemia that occurs when the body's stored iron is depleted and cannot meet the needs for normal red blood cell production. Before the production of red blood cells is limited, the body's stored iron has already been exhausted. However, at this stage, the routine blood tests may not yet show obvious signs of anemia; this condition is then referred to as iron deficiency. The characteristics of iron deficiency anemia include a lack of stainable iron in the bone marrow and other tissues, as well as reduced serum ferritin and transferrin saturation, presenting as typical microcytic hypochromic anemia. Therefore, iron deficiency anemia is a type of microcytic hypochromic anemia and is classified according to the level of marrow proliferation as a hyperproliferative anemia.