Total iron binding capacity
Total iron binding capacity (TIBC) is an indirect measurement of transferrin receptors in blood and in bone marrow. It is one of the basic tests used in the differential diagnosis of anemia, the other major biochemical measurements being serum iron (SI), and serum ferritin. While the test is in widespread use, direct transferrin receptor measurement tests are becoming available for clinical practice.
Since transferrin is the only iron-binding protein involved in iron transport, TSAT predicts the availability of iron to the bone marrow.
TIBC is calculated as the sum of unsaturated iron binding capacity (UIBC) and serum iron. Unsaturated iron binding capacity is directly measured by adding a known amount of iron to serum, and measuring the amount of iron that does not bind to transferrin receptors.
Among its clinical applications is distinguishing pure iron deficiency anemia from anemia of chronic disease. The two can coexist, and iron deficiency anemia can also be present but present ambiguous laboratory values in the presence of any inflammation, not necessarily enough to produce classic anemia of chronic disease. Newer tests becoming more widely available, such as soluble tranferrin receptor (sTfR), definitely supplement it. In addition, some tests in limited availability, such as reticulocyte hemoglobin content and the percentage of hypochromic red cells also appear to be clinically useful. Hepcidin measurement is still a research tool but also may help in the presence of inflammation.