PTH and chronic kidney disease: Parathormone (PTH), calcitriol or 1, 25(OH)2D3 (the natural most active form of the hormonal system of vitamin D), calcidiol or 25(OH)D3 (substrate of calcitriol), calcitonin and fibroblast growth factor 23 (FGF23)/klotho are the classical key calciotropic hormones regulating calcium and phosphate in CKD patients6.