FNDC5 and chronic kidney disease: After adjusting for an age ≥ 64 years and the presence of atrial fibrillation, diabetes mellitus, CKD stages 1–3 and dilated cardiomyopathy (Model 2), the multivariable Cox regression analysis revealed that a level of irisin ≤ 7.2 ng/mL was an independent predictor of the cumulative clinical endpoint.