Clinical significance of FGF-23 measurement in dialysis patients

AIMS: Considering the growing relevance of fibroblast growth factor-23 (FGF-23) in the pathogenesis of chronic kidney disease bone and mineral disorder (CKD-MBD), an analysis was performed to determine the relative importance of C-terminal (cFGF-23) and intact (iFGF-23) assays in assessing CKD-MBD status in the first place and the relationship between FGF-23 and mortality as a secondary aim. METHODS: In 77 patients (15 peritoneal dialysis and 62 hemodialysis), levels of calcium, phosphate, parathyroid hormone (PTH), 25-hydroxyvitamin- D (25D), 1,25D, FGF-23 (C-terminal and intact molecule) were measured and their correlations were analyzed. The relationship between FGF-23 levels and patient survival was also analyzed. RESULTS: A significant correlation was found between cFGF-23 and 1,25D, PTH and 25D while iFGF-23 was significantly correlated with phosphate, 25D and PTH. PTH and 1,25D were independent predictors of cFGF-23, while for iFGF-23 independent predictors were phosphate and 25D. No significant relationship was found between FGF-23 and mortality. CONCLUSIONS: C-terminal or intact FGF-23 levels are weakly correlated and thus not clearly indicative of FGF-23 effects on PTH, P and vitamin D metabolism in dialysis patients. Assays for cFGF-23 and iFGF-23 showed a good correlation, but the intact molecule was not superior in defining interactions with CKD-MBD molecules. Measuring FGF-23 on a regular basis with the current assays in CKD and dialysis patients does not yet seem clinically useful.