FGF23 Elevation and Hypophosphatemia after Intravenous Iron Polymaltose: A Prospective Study

Context: Parenteral iron administration has been associated with hypophosphatemia. Fibroblast growth factor 23 (FGF23) has a physiological role in phosphate homeostasis via suppression of 25-hydroxyvitamin D [25(OH)D] activation and promotion of phosphaturia. We recently reported a case of iron-induced hypophosphatemic osteomalacia associated with marked FGF23 elevation. Objective: Our objective was to prospectively investigate the effect of parenteral iron polymaltose on phosphate homeostasis and to determine whether any observed change was related to alterations in circulating FGF23. Design, Setting, and Participants: Eight medical outpatients prescribed iv iron polymaltose were recruited. Plasma phosphate, 25(OH)D, 1,25-dihydroxyvitamin D [1,25(OH)2D], PTH, FGF23, and urinary tubular reabsorption of phosphate were measured prior to iron administration and then weekly for a minimum of 3 wk. Results: Plasma phosphate fell from 3.4 ± 0.6 mg/dl at baseline to 1.8 ± 0.6 mg/dl at wk 1 (P < 0.0001) associated...