Low serum ferritin means that the concentration of serum ferritin in the body is below the normal range. Normal serum ferritin concentration is 15-200ug/L for adult males and 12-150ug/L for adult females. A lower serum ferritin concentration indicates that the body has insufficient stored iron. Ferritin is a complex formed by deferrin and trivalent iron ions, which is the most important form of iron storage in the body, and it maintains the supply of iron in the body while maintaining the stability of hemoglobin concentration. When iron deficiency occurs, such as insufficient intake, impaired absorption, and chronic blood loss, resulting in the inability to reabsorb iron, the body’s serum ferritin concentration decreases significantly, and when iron supplementation therapy is given, the body’s serum ferritin concentration increases significantly.