The serum iron level represents the amount of circulating iron bound to transfer- rin. The TIBC is an indirect measure of the circulating transferrin. The normal range for the serum iron is 50–150 μg/dL; the normal range for TIBC is 300–360 μg/dL. Transferrin saturation, which is normally 25–50%, is obtained by the following formula: serum iron × 100 ÷ TIBC. Iron-deficiency states are associated with saturation levels <0%. There is a diurnal variation in the serum iron. A transferrin saturation >50% indicates that a disproportionate amount of the iron bound to trans- ferrin is being delivered to nonerythroid tissues. If this persists for an extended time, tissue iron overload may occur.