Ferritin below the normal range indicates depletion of iron stores and possible iron deficiency. In healthy subjects, low serum ferritin correlates well with iron deficiency. However, ferritin is an acute-phase protein that can be elevated in response to inflammation. Patients with anemia of chronic disease may have an elevated ferritin concentration due to inflammation. The transit pool is measured directly as serum iron and transferrin.
Serum iron tends to be lower in both iron deficiency and inflammatory conditions.
TIBC tends to be elevated in iron deficiency and lower in inflammatory conditions and chronic disease states. For otherwise healthy patients, ferritin, serum iron, and TIBC are adequate for measuring iron status. However, for patients who have inflammatory, infectious, or malignant disease, measurement of the usual parameters of iron status may not be sufficient for differentiating iron deficiency anemia from anemia of chronic disease. The most definitive assessment of iron status in these cases is a bone- marrow aspirate stained for iron. In instances where bone marrow biopsy is not desirable due to a number of reasons, such as invasiveness or inability to obtain an adequate aspirate, a measurement of serum soluble transferrin receptor may be helpful.