Iron and Total Iron-binding Capacity (TIBC)

Iron and Total Iron-binding Capacity (TIBC) testing, which includes serum iron, TIBC, unsaturated iron-binding capacity (UIBC), and transferrin saturation, supports the workup of microcytic or hypochromic anemia and helps differentiate iron deficiency from anemia of chronic disease. It contributes to the evaluation of thalassemia and sideroblastic anemia, the assessment of suspected hereditary hemochromatosis and other iron overload states, investigation of acute iron ingestion, and monitoring of iron balance in patients on chronic dialysis or receiving transfusions. Transferrin or TIBC can reflect nutritional status, and percent transferrin saturation often provides more clinical insight than serum iron alone in suspected deficiency. Interpretation is integrated with ferritin and the presence of inflammation, as infection, inflammatory conditions, malignancy, and liver disease can alter iron and transferrin concentrations.

Intestinally absorbed iron circulates bound to transferrin and is used primarily for erythropoiesis; the majority of body iron resides within hemoglobin, with reserves stored as ferritin and hemosiderin. Iron depletion evolves from reduced stores to iron-restricted erythropoiesis and ultimately to overt iron deficiency anemia, whereas excess iron can injure the liver, heart, and pancreas. Serum iron shows diurnal fluctuation and biologic variability, so results are interpreted alongside TIBC or transferrin, transferrin saturation, and ferritin. Low serum iron does not invariably indicate true deficiency in the setting of acute or chronic inflammation, infection, malignancy, or renal disease, and ferritin is often increased in these conditions. When absolute deficiency must be established, bone marrow iron remains the most sensitive indicator.