What is Total Iron Binding Capacity (TIBC) and Unsaturated Iron Binding Capacity (UIBC)?
Total Iron Binding Capacity is an indirect measure of transferrin concentration — it quantifies the maximum amount of iron that serum transferrin can bind. In iron deficiency, the liver upregulates transferrin synthesis to maximise iron capture from the depleted pool, raising TIBC above the reference range. In inflammatory states and chronic disease, transferrin is downregulated as a negative acute phase reactant, reducing TIBC. UIBC (unsaturated iron binding capacity) represents the unoccupied transferrin iron-binding sites — the spare binding capacity — and together with serum iron allows calculation of transferrin saturation: Transferrin Saturation (%) = (Serum Iron ÷ TIBC) × 100.