In the measurement of Total Iron Binding Capacity (TIBC), what is the purpose of saturating transferrin with ferric iron?

• A. Saturate all transferrin binding sites with ferric iron
• B. Remove excess iron from transferrin by dialysis
• C. Increase transferrin protein concentration by ultrafiltration
• D. Precipitate iron using magnesium carbonate

Answer: (A)

The measurement of TIBC hinges on assessing how much iron transferrin could carry when fully loaded. Saturating transferrin with ferric iron fills every iron-binding site, so the test reflects the maximum capacity of transferrin to bind iron rather than how much iron is currently bound in the body. By filling all sites, you can then remove any unbound iron and quantify the iron that remains bound, which corresponds to the total binding capacity. If sites aren’t fully occupied, you’d underestimate how much iron transferrin is capable of binding.