FGF23 and chronic kidney disease: In this review, we will describe the potentially deleterious effects of FGF23 in CKD; summarize the published data from clinical trials in adults evaluating ferric citrate in CKD; and present the background, hypotheses, and design features of the NIDDK-funded Ferric Citrate and Chronic Kidney Disease in Children (FIT4KiD) study, a 12-month, double-blind, randomized, placebo-controlled trial to evaluate the effects of ferric citrate on changes in FGF23 levels in pediatric patients with CKD stages 3–4.