Serum Iron and Total Iron-Binding Capacity The serum iron level represents the amount of circulating iron bound to transferrin. The TIBC is an indirect measure of the circulating transferrin. The normal range for the serum iron is 50-150 mg/dL; the normal range for TIBC is 300-360 mg/dL. Transferrin saturation, which is normally 25-50%, isobtained by the following formula: serum iron x 100 / TIBC. Iron deficiency states are associated with saturation levels below 20%. There is a diurnal variation in the serum iron. A transferrin saturation % >50% indicates that a dispropoionate amount of the iron bound to transferrin is being delivered to nonerythroid tissues. If this persists for an extended time, tissue iron overload may occur.Ref: Harrison&;s Principles of Internal Medicine; 19th edition; Chapter 126 Iron Deficiency and Other Hypoproliferative Anemias; Page no: 627