Time-averaged level of fibroblast growth factor-23 and clinical events in chronic kidney disease.

BACKGROUND A single time-point fibroblast growth factor-23 (FGF23) level is a strong, well-established risk factor for clinical events in chronic kidney disease (CKD). This study investigated whether repeated measurements of FGF23 after 2 years, allowing the calculation of time-averaged FGF23 and the rate of change in FGF23, provided a better prediction of clinical events in CKD than a single time-point value. METHODS A post-hoc analysis was performed in a subset of 439 adult patients with a median estimated glomerular filtration rate of 36 (interquartile range 28-48) mL/min per 1.73 m(2) of the prospective multicentre MASTERPLAN study, in which paired samples to measure FGF23 were available. The primary outcome was defined as a composite of myocardial infarction, stroke and cardiovascular mortality and secondary end points, which were overall mortality, congestive heart failure (CHF) and start of renal replacement therapy. Only events occurring after Month 24 were included in the analysis. RESULTS Analysis of different FGF23 measures showed that a single time-point value and time-averaged FGF23 were positively associated with the primary end point, and also with overall mortality, start of renal replacement therapy and CHF. The adjusted hazard ratios of a single value of FGF23 and of time-averaged FGF23 for the composite end points were 1.71 (CI 1.20-2.43) and 1.91 (CI 1.29-2.82), respectively. Change in FGF23 was not associated with any outcome except for the initiation of renal replacement therapy. CONCLUSIONS Our study confirms that FGF23 is an important cardiovascular risk factor. Two measurements of FGF23 have no added value over a single value to predict the cardiovascular outcome. This study demonstrates that, under routine clinical practice, the variability of FGF23 in 2 years' time is small. Concomitantly, this study showed no benefit of consecutive FGF23 testing for estimating the risk of a clinical event in an individual patient.