FGF23 and osteomalacia: Modern formulations of IV iron enable a large dose to be administered safely with a low complication rate comparable to other infusions.1 However, ferric carboxymaltose (FCM) can cause hypophosphatemia mediated by fibroblast growth factor 23 (FGF23) that increases urinary excretion of bone phosphate.2 While this is often an asymptomatic laboratory finding, concern has arisen from reports of osteomalacia and bone fractures.3