However, the inadequate response to erythropoietic therapy has not been well-characterized through rigorous studies and hence remains poorly handled in routine clinical practice. A major cause for not responding to EPO treatment is likely functional iron deficiency (FID), which is defined as a failure to provide iron to the erythroblasts despite sufficient iron stores. Patients with FID require supplementation of usable iron to optimize response to erythropoietic therapy, which might not be accomplished with oral iron. In a recent prospective, open-label trial, patients receiving epoetin alfa for CIA who were treated with IV iron dextran had a significantly greater Hb response compared with those receiving oral iron. Meanwhile, in patients with CIA and no iron deficiency, IV iron supplementation significantly reduced treatment failures to darbepoetin without additional toxicity. However, whether that IV iron supplementation increases the risk of disease progression, incidence of thrombosis and heart failure as well as iron overload, is under careful investigation. Though the association between IV iron and serious AEs and mortality remains unclear, Zitt et al. found that the use of IV iron was associated with a 22% reduction in mortality. Therefore, investigators designed this multicentre, randomized trial to investigate EPOs in combination with IV iron with regard to an increase of Hb levels in patients who have inadequate responses to initial treatment with routine doses of EPOs.