FGF23 and secondary hyperparathyroidism: Derangements induced by CKD are multiple, ranging from the classically described disturbances of vitamin D metabolism, calcium, and phosphate balance, through increased levels of parathyroid hormone (PTH) (secondary hyperparathyroidism) to the more recently recognized increases in fibroblast growth factor 23 (FGF23) and sclerostin, or decreased serum klotho levels, among others (Kidney Disease: Improving Global Outcomes KDIGO CKD-MBD Update Work Group, 2017; Llach et al., 2000; Hruska et al., 2017).