Many patients who have borderline low iron stores at the start of ESA therapy develop absolute iron deficiency as these stores become depleted during the production of new red blood cells. Others with adequate or even excessive iron stores may develop FID. The latter occurs when sufficient amounts of iron cannot be released from its reserves, mostly the reticuloendothelial system (RES) to satisfy
the increased demand of the bone marrow during ESA-induced erythropoiesis, as this website is often the case in ACD [20, 21]. FID is the most common cause of suboptimal ESA response, leading physicians to use IV iron to improve its availability [24, 25]. The previous belief that IV iron therapy would become progressively inefficient with increasing serum pretreatment ferritin levels, and be practically useless with pretreatment ferritins >500 ng/ml  has been contradicted by a recent trial, the Dialysis Patients’ Response to IV iron with Elevated ferritin (DRIVE) study . The authors of this study demonstrated that IV ferric gluconate administration was superior to no iron treatment in improving hemoglobin levels in ARN-509 molecular weight anemic hemodialysis patients with ferritin levels of 500–1200 ng/ml
and transferring saturation (TSAT) >25 %. The conclusion from observations such as Rigosertib mouse this one is that intravenous iron administration can effectively raise Hb even in patients with elevated iron stores. Following the report of the DRIVE study, there has been a tendency towards increasing the upper limit of serum ferritin levels. However, it must be emphasized that there is no proof at present that pushing up Hb levels with excessive
iron doses improves the vital prognosis of MHD patients. It could even do the opposite. Transfer of intravenous iron to erythroid cells We do not completely understand the exact mechanism involved in the improvement of Hb levels or ESA response subsequent to IV iron administration. Based on previous pharmacokinetic studies, however, one can speculate how parenteral however iron may be utilized for erythropoiesis. The pharmacokinetics of parenteral iron sucrose or iron–polysaccharide complexes have been assessed using positron emission tomography [28, 29]. These studies demonstrated that non-saturation of the transport system allows iron transfer from the blood to the bone marrow, indicating the presence of a large interstitial transport pool. Similar observations were reported in previous ferrokinetic studies using radiolabeled iron (59Fe) where time-dependent accumulation of 59Fe was detected over the sacrum, a site of hematopoietic marrow . Erythroid precursors have an extremely high iron requirement, especially during Hb synthesis.