FGF23 and kidney failure: This study focused on adolescents with a mean age of 14 years and no renal failure,17 Wojcik et al. reported an inverse correlation between insulin resistance and FGF-23.18 In another study they conducted on obese adolescents with insulin resistance and without renal failure, they reported lower FGF-23 levels when compared to obese controls who did not have insulin resistance.