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Absolute iron deficiency may be diagnosed when TSAT is <20% and SF is <100 ng/mL.2 Functional iron deficiency may be more difficult to diagnose since iron status parameters may indicate adequate iron stores. Patients on epoetin with functional iron deficiency have TSAT <20% and normal serum ferritin levels (≥100 ng/mL) but experience hemoglobin or hematocrit decreases at the same or an increased epoetin dose. Patients with functional iron deficiency will usually experience an increase in hemoglobin/hematocrit after a course of IV iron therapy. Functional iron deficiency also must be differentiated from inflammatory iron block, which can also occur in patients with chronic inflammatory conditions such as infections, certain malignancies, and autoimmune disorders. In this case, both hemoglobin and hematocrit are reduced, and TSAT may be <20%.2 SF levels, on the other hand, may be 100 to 700 ng/mL or higher. In patients with functional iron deficiency, serial levels of SF decrease during epoetin alfa therapy, yet remain elevated (≥100 ng/mL); in contrast, patients with inflammatory iron block usually show an abrupt increase in SF along with a sudden drop in TSAT.2 The level of C-reactive protein can also indicate the presence of inflammatory iron block and may help distinguish this condition from true functional iron deficiency. The table below details how laboratory parameters differ under conditions of absolute iron deficiency, functional iron deficiency, and inflammatory iron block. Laboratory Parameters Under Conditions of Absolute Iron Deficiency, Functional Iron Deficiency, and Inflammatory Iron Block
* Has not been evaluated.
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