FGF23 and chronic kidney disease: The correlation coefficient for the association between FGF23 and α-Klotho was 0.81 (P = 0.743), 0.12 (P = 0.837), -0.12 (P = 0.080), -0.03, (P = 0.670), 0.11 (P = 0.304), and -0.24 (P = 0.443) among patients who had CKD stage G1, G2, G3a, G3b, G4, and G5, respectively.