Iron-Binding Capacity, Total (TIBC)

TIBC measures the bloods capacity to bind iron with transferrin (TRF). One milligram of TRF binds to 1.25 Ž ¼g of iron, and, therefore, a serum TRF level of 300 mg/dL is equal to TIBC of (300 ƒ — 1.25) 375 Ž ¼g/dL. TIBC is an indirect way of assessing TRF level. TIBC correlates with serum TRF, but the relationship is not linear over the wide range of TRF values and is disrupted in diseases affecting transferrin-binding capacity and iron-binding proteins. TIBC should not be confused with unsaturated binding capacity (UIBC), where UIBC = TIBC minus serum iron ( Ž ¼g/dL).

Normal range: 255 " “450 Ž ¼g/dL.

Use

Differential diagnosis of anemias

Should always be performed whenever serum iron is done to calculate percent saturation for diagnosis of iron deficiency

Screening for iron overload

Acute hepatitis

Late pregnancy

Interpretation

Increased In

Iron deficiency

Acute and chronic blood loss

Acute liver damage

Late pregnancy

Progesterone birth control pills

Decreased In

Hemochromatosis

Cirrhosis of the liver

Thalassemia

Anemias of infection and chronic diseases (e.g., uremia, RA, some neoplasms)

Nephrosis

Hyperthyroidism

Limitations

Estrogens and oral contraceptives increase TIBC levels.

Asparaginase, chloramphenicol, corticotropin, cortisone, and testosterone decrease the TIBC levels.