Association of serum levels of FGF23 and α-Klotho with glomerular filtration rate and proteinuria among cardiac patients

BACKGROUND Expression and/or excretion of fibroblast growth factor-23 (FGF23) and its co-receptor Klotho are altered in patients with end-stage renal disease. The possibility that the FGF23/α-Klotho system mediates the aggravated cardiovascular outcome among patients with chronic kidney disease (CKD) has been suggested. We determined whether FGF23 and α-Klotho concentrations are altered among patients with reduced renal function and proteinuria. METHODS Serum FGF23 and α-Klotho were measured in cardiology patients who were not undergoing chronic hemodialysis. Estimated glomerular filtration rate (eGFR) was correlated negatively with FGF23 and positively with α-Klotho. RESULTS The correlation between FGF23 and the renal tubular maximum reabsorption rate of phosphate to the GFR (TmP/GFR) was not significant, but that between FGF23 and serum calcium or inorganic phosphate was significant among patients with an estimated GFR of less than 60 mL/min/m(2). By stepwise multivariate regression analysis, eGFR was selected as significant predictor for FGF23 or α-Klotho among patients with an estimated GFR of less than 60 mL/min/m(2); however, urine albumin/creatinine ratio was not selected as a predictor for FGF23 or α-Klotho irrespective of the eGFR levels. In patients with eGFR of <60 mL/min/1.73 m(2), UACR was significantly associated with log(FGF23); but, this association did not remain statistically significant in a multivariate model. CONCLUSIONS Among cardiology patients with various stages of CKD, serum concentrations of FGF23 and α-Klotho were associated with renal function, but not with the extent of proteinuria.