FGF23 and hyperphosphatemia: Subsequently, the progressive decreased calcium levels or increased phosphate levels in advanced CKD stages induce overactive parathyroid glands, called secondary hyperparathyroidism (SHPT), that is typically characterised by hypocalcaemia, hyperphosphataemia, elevated fibroblast growth factor-23 (FGF-23), reduced 1,25-dihydroxy vitamin D3 [1,25(OH)2D3] and high parathyroid hormone (PTH) levels.3