[How do we optimally evaluate iron stores in dialyzed patients treated with erythropoiesis stimulating agent?]

The treatment of renal anaemia with erythropoiesis stimulating agent is often associated with a functional iron deficiency characterized by normal or elevated iron stores but insufficient iron delivered for erythropoiesis. Biological markers of iron status depend on the compartment where it is located: stored, circulating or available for erythropoiesis. Ferritin is the protein of iron storage but also a protein of the acute phase of inflammation and serum ferritin increases in case of liver cytolysis. In the circulation iron is bound to transferrin (Tf). Tf dosage is necessary to calculate transferrin saturation coefficient (TSAT) which decreases below 20% in iron deficiency but also in inflammatory states. Another Limitation is the nycthemeral variations of serum iron. The best marker of functional iron deficiency is the percentage of hypo chromic red cells (> 6%) followed by reticulocyte Hb content (< 29 pg/cell). These 2 markers measure the body capacity to donate iron to erythroid precursors but necessitate specific laboratory equipment. In all cases evaluation of iron balance should be done at least eight days after the last iron infusion.