The association between Fibroblast Growth Factor 23 and renal transplantation outcome is modified by follow-up duration and glomerular filtration rate assessment method

Introduction Fibroblast growth factor 23(FGF23) could contribute to cardiovascular morbidity in chronic kidney disease. In studies of kidney transplant recipients, a high circulating level of FGF23 has been associatedwith death and graft loss independently of estimated glomerular filtration rate (GFR). Whether FGF23 is associatedwith adverse outcomes in the early posttransplantation period is unknown. Methods We analyzed a cohort of 845 kidney transplant recipients in stable condition who had GFR measured in the first years after transplantation with a median follow-up of 71 months. Results A high FGF23 concentration was associatedwith death or graft loss in univariate analysis, but this associationwas lost after adjustment for measured GFR. In contrast, FGF23 remained significantly associatedwith the composite outcome when estimated GFR was substituted for measured GFR. We also observed that follow-up duration modified the associationbetween FGF23 and outcome. Although FGF23 was not associatedwith any endpoint in the full duration of the study, we found an independent associationbetween FGF23 and the incidence of graft loss within the 4 years after FGF23 measurement. We did not find an associationbetween FGF23 levels and left ventricular mass in a subgroup of 227 patients who had echocardiography performed within 3 months of FGF23 measurement. Discussion This study demonstrates that FGF23 measured during the first year after transplantation is not an independent predictor of death and graft loss and is not associatedwith left ventricular hypertrophy in the posttransplantation period. It further unveils important factors modifying the associationbetween FGF23 and outcome in this population.