Originally I was thinking it might be low due to your body making more RBC's and using up the serum iron, so I went on to find more info before I posted..
Iron plays a principal role in erythropoiesis. It is necessary for proliferation and maturation of red blood cells and for hemoglobin (Hgb) synthesis. Of the body's normal 4 g of iron (less in women), about 65% is present in Hgb and about 3% in myoglobin. A small amount is also found in cellular enzymes that catalyze the oxidation and reduction of iron. The remainder of iron is stored in the liver, bone marrow, and spleen as ferritin or hemosiderin. Any iron present in the serum is in transit among the alimentary tract, the bone marrow, and available iron storage forms. Iron travels in the bloodstream bound to transport proteins. Transferrin is the major iron-transport protein, carrying 60% to 70% of the body's iron. For this reason, total iron-binding capacity (TIBC) and transferrin are sometimes referred to interchangeably, even though other proteins carry iron and contribute to the TIBC. Unbound iron is highly toxic, but there is generally an excess of transferrin available to prevent the buildup of unbound iron in the circulation. The percentage of iron saturation is calculated by dividing the serum iron value by the TIBC value and multiplying by 100.
•Drugs that may decrease TIBC levels include asparaginase, chloramphenicol, corticotropin, cortisone, and testosterone.