Leaf DE, et al. - Whether there exists a prospective association of elevated plasma levels of the osteocyte-derived, vitamin D–regulating hormone, fibroblast growth factor 23 (FGF23), with death in critically ill patients with AKI requiring RRT, and in a general cohort of critically ill patients with and without AKI, was investigated. Higher FGF23 levels were shown to be independently related to greater mortality in critically ill patients.