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) is typically ordered along with the SI. These determinations are helpful 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 increased in iron deficiency anemia.
Serum transferrin can be measured directly using immunochemical methods such as nephelometry and turbidimetry. TIBC is performed in a 2-step method by adding sufficient ferric iron to the specimen to fill all of the iron-binding sites on transferrin completely. Absorption with magnesium carbonate, alumina, or ion resin removes excess, unbound iron. The iron content of the saturated binding protein is then measured as described for SI. TIBC is calculated to measure the unsaturated iron-binding capacity (UIBC) in many analytical systems.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
