PTH and chronic kidney disease: The normalization of serum phosphate concentrations in early stages of CKD may be mainly mediated by compensatory decreases in circulating concentrations of 1,25(OH)2D and increases in circulating concentrations of iFGF23 and PTH, while the phosphatonin iFGF7 may not play a crucial role in the compensatory response to phosphate retention in CKD-MBD.