Fibroblast Growth Factor 23 and Klotho in Cardiac Surgery-Associated AKI

Background: Acute kidney injury (AKI) frequently occurs as a complication following cardiac surgery, leading to increased mortality and prolonged hospital stays. Elevated serum FGF23 levels have been suggested to be associated with a greater degree of systemic inflammation in critical ill patients. This study aims to evaluate the roles of serum FGF23 and klotho levels post-cardiac surgery, and to determine their impact on the occurrence of severe AKI in these patients. Methods: We included adult patients who underwent on-pump cardiac surgery in a tertiary care university hospital. All prospective clinical and laboratory data were evaluated as predictors of AKI. Serum FGF23 and klotho level were measured within 6 hours after cardiac surgery. The discriminative power for predicting severe AKI (stage 2 or 3) was assessed using the area under the receiver operator characteristic curve (AUROC). Results: We investigated 214 adult patients with a mean age of 59.9 year. Severe AKI was diagnosed in 32 patients (15.0%). Patients with severe AKI had longer bypass time. Higher FGF23 level and lower klotho level were independent risk factors for severe AKI, even after adjustment for clinical risk factors. The clinical prediction model for severe AKI had an AUROC of 0.71. Adding FGF23 to the clinical model increased the AUROC for predicting severe AKI to 0.76, while combining FGF23 and klotho increased it further to 0.79. The optimal cutoff values for FGF23 and klotho is 2264 pg/ml and 100 pg/ml, respectively. We also performed ROC analysis of the single serum FGF23/klotho ratio, which revealed an AUROC value of 0.71, with a sensitivity of 62.5% and a specificity of 80.2% for predicting severe AKI at a threshold value of 29.5. Conclusion: The combination of elevated FGF23 level and reduced klotho level could serve as a potential biomarker for the predicting severe AKI.