Under normal circumstances, serum iron can only bind to 1/3 of the transferrin, 2/3 of the transferrin failed to bind to iron, and the transferrin that is not bound to iron is called unsaturated iron binding capacity, and the maximum amount of iron that can be bound to transferrin per liter of serum is called the total iron binding capacity, that is, the sum of serum iron and the unsaturated iron binding capacity. Common causes of decreased total iron binding capacity include: i. Decreased synthesis of transferrin, such as cirrhosis, chronic liver disease, etc. ii. Loss of transferrin, such as nephrotic syndrome. Iron deficiency, such as liver disease, chronic inflammation, peptic ulcer and so on.