Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. The transferrin saturation test (TSAT) refers to the ratio of serum iron to total iron-binding capacity, expressed as a percentage. Transferrin saturations of less than 20% indicate iron deficiency, while transferrin saturations of more than 50% suggest iron overload. Note that the results of the TSAT can be influenced by inflammation.