Unsaturated iron binding capacity

The serum unsaturated iron binding capacity and total iron binding capacity (TIBC) are determined by addition of sufficient Fe to saturate iron binding sites on transferrin. The excess Fe " is removed (e.g., by adsorption with light magnesium carbonate [MgCOs] powder), and the assay for iron content is then repeated. From this second measure-... 

Because normally only about one third of the iron binding sites of transferrin are occupied by Fe ", serum transferrin has considerable reserve iron binding capacity. This is called the serum unsaturated iron binding capacity. The TIBC is a measurement of the maximum concentration of iron that transferrin can bind. The serum TIBC varies in disorders of iron metabolism. It is often increased in iron deficiency and decreased in chronic inflammatory disorders or malignancies, and it is often decreased also in hemochromatosis. 

International Committee for Standardization in Haematology. The measurement of total and unsaturated iron binding capacity in serum. Br J Haematol 1978 38 281-94. 

Plasma iron determinations are of little value in these cases because plasma iron is decreased in thalassemia and anemia resulting from infection. In contrast, an increase in the unsaturated iron binding capacity of the plasma is pathognomonic for iron deficiency. The cytological examination of a bone marrow smear stained for iron, however, is the most reliable method of diagnosis. Iron-stain cells are absent from the marrow of iron-deficient patients (see Fig. 6-8). 

---