The test for Tf measures the concentration of the primary carrier protein for iron. Measuring or calculating TIBC is an indirect method of assessing transferrin and provides comparable information. The TIBC (or transferrin) are typically ordered along with the SI. Taken together, these determinations are useful in the differential diagnosis of many disorders affecting iron metabolism, including HH and iron deficiency anemia. Tf and TIBC are typically low-normal or decreased in HH and are increased in iron deficiency.
Serum transferrin can be measured directly using immunochemical methods such as nephelometry and turbidimetry. TIBC is performed in a 2-step method by adding ferric iron to the specimen in sufficient quantity to completely fill all of the iron binding sites on transferrin. Excess, unbound iron is removed by adsorption with magnesium carbonate, alumina, or ion resin. The iron content of the saturated binding protein is then measured as described for SI. In many analytical systems, TIBC is calculated based on measuring the unsaturated iron binding capacity (UIBC). (2)
Serum is the specimen of choice for Tf and TIBC. TIBC is less subject than SI to day-to-day variation and other causes of variability.
A typical reference interval for TIBC is 300 - 360 µg/dL.(2)