Fibroblast growth factor -23 (FGF-23) is a key regulator of mineral metabolism. It regulates renal phosphate (Pi) reabsorption and calcitriol synthesis, and has an inhibitory effect on parathyroid hormone (PTH) secretion. FGF-23 increases early in chronic kidney disease (CKD), but the regulation of FGF-23 in mild -to -moderate renal dysfunction is not fully understood.