KL and chronic kidney disease: When we evaluated s-Klotho in the different CKD stages, we found reduced levels since CKD stage 2, with a more significant reduction in CKD stages 3 and 4 (reference values = 845 ± 330, pg/mL; stage 2 = 611 ± 191, pg/mL, P < .01; stage 3 = 529 ± 160, pg/mL, P < .001; stage 4 = 393 ± 142, pg/mL; P < .001.