PTH and autosomal dominant polycystic kidney disease: In patients with ADPKD, levels of the phosphaturic hormone fibroblast growth factor 23 (FGF-23) are 2- to 3-fold higher compared with those with non-ADPKD chronic kidney disease (CKD) and 6-fold higher compared with healthy subjects despite similar levels of parathyroid hormone (PTH), vitamin D and serum calcium [2–5].