Effects of modest iron loading on iron indices in healthy individuals

Intravenous iron administration is typically indicated in individuals who have iron deficiency refractory to oral iron. However, in certain chronic disease states such as heart failure, it may be beneficial to administer intravenous iron to individuals who are not strictly iron deficient. The purpose of this study was to define a dose-response relationship between clinical indices of iron status and modest loading with intravenous iron in healthy, iron-replete participants. This was a double-blind, controlled study involving 18 male participants. Participants were block-randomized 2:1 to the iron and saline (control) groups. Participants in the iron group received 3.75 mg/kg body wt up to a maximum of 250 mg of intravenous iron, once a month for 6 mo, provided that their ferritin remained measured <300 µg/l within the week before a dose was due and their transferrin saturation remained <45%. Otherwise they received a saline infusion, as did the control participants. Iron indices were measured monthly during the study. The pulmonary vascular response to sustained hypoxia and total hemoglobin mass were measured before, at 3 mo (hemoglobin mass only), and at 6 mo as variables that may be affected by iron loading. Serum ferritin was robustly elevated by intravenous iron by 0.21 µg·l^-1·mg^-1 of iron delivered (95% confidence interval: 0.15-0.26 µg·l^-1·mg^-1), but the effects on all other iron indices did not reach statistical significance. The pulmonary vascular response to sustained hypoxia was significantly suppressed by iron loading at 6 mo, but the hemoglobin mass was unaffected. We conclude that the robust effect on ferritin provides a quantitative measure for the degree of iron loading in iron-replete individuals.NEW & NOTEWORTHY There has been an increasing interest in administering intravenous iron to patients to alter their iron status. Here, we explore various indices of iron loading and show that in healthy volunteers serum ferritin provides a robust indicator of the amount of iron loaded, with a value of 21 µg/l increase in ferritin per 100 mg of iron loaded.