FGF23 and chronic kidney disease: In fact, during the course of CKD, the progressive decrease in GFR leads to phosphate retention; however, it has been demonstrated that serum phosphate level may remain normal until the advances stages of CKD [10] due to a compensatory increase in PTH and fibroblast growth factor 23 (FGF-23), two pivotal main hormones involved in the regulation of renal phosphate handling [11].