FGF23 and chronic kidney disease: Currently, there is stillcontroversy as to whether serum Klotho levels increase or decrease with theprogression of CKD, and whether ELISA assays are reliable.10 Nor have we found the impact of smoking on FGF-23 levels,contrary to what has been described previously.11 This result could be explained by the use of different assays, sincewe measured the intact molecule and these authors evaluated the C-terminal fractionof FGF-23.