PTH and chronic kidney disease: Over the years, different pathophysiological theories have been presented; however, once fibroblast growth factor 23 (FGF-23) and Klotho were discovered, it could be explained why, in the absence of hyperphosphatemia (normal values of phosphate being maintained by the increased levels of FGF-23 in the initial stages of CKD), PTH levels would increase (Figure 1) [8,11].