Which of the following is true about iron deficiency anemia

Ref Harrison 19 th ed pg 627 The serum iron level repre- sents 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%, is obtained 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.