Recurrent severe hypophosphatemia following intravenous iron administration.

Hypophosphatemia postintravenous iron is frequent but under-recognized. If prolonged or recurrent, it can cause osteomalacia. The likely mechanisms are direct toxicity to proximal tubular cells causing phosphate wasting, elevated Fibroblast growth factor-23 (FGF-23), and reduced 1,25-dihydroxyvitamin D (1,25(OH)2D). Hypophosphatemia may be severe and persist for months, necessitating phosphate replacement until normalization of serum levels occurs.