Under normal conditions, serum iron can only bind 1/3 of transferrin, 2/3 of transferrin fails to bind iron, the unsaturated iron binding capacity is called unsaturated iron binding capacity, the maximum amount of iron that can be bound by transferrin per liter of serum is called total iron binding capacity, which is the sum of serum iron and unsaturated iron binding capacity. The common reasons for the decrease in total iron binding capacity are: a. Decrease in transferrin synthesis, such as cirrhosis, chronic liver disease, etc. Second, transferrin loss, such as nephrotic syndrome. Third, iron deficiency, such as liver disease, chronic inflammation, peptic ulcer and other causes of iron deficiency.