FGF23 and chronic kidney disease: 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