Fibroblast growth factor 23 in patients undergoing peritoneal dialysis

Abstract

Background and objectives: Fibroblast growth factor 23 (FGF23) is an independent risk factor for mortality in patients with ESRD. Before FGF23 testing can be integrated into clinical practice of ESRD, further understanding of its determinants is needed.

Design, setting, participants, & measurements: In a study of 67 adults undergoing peritoneal dialysis, we tested the hypothesis that longer dialysis vintage and lower residual renal function and renal phosphate clearance are associated with higher FGF23. We also compared the monthly variability of FGF23 versus parathyroid hormone (PTH) and serum phosphate.

Results: In unadjusted analyses, FGF23 correlated with serum phosphate (r = 0.66, P < 0.001), residual renal function (r = -0.37, P = 0.002), dialysis vintage (r = 0.31, P = 0.01), and renal phosphate clearance (r = -0.38, P = 0.008). In adjusted analyses, absence of residual renal function and greater dialysis vintage associated with higher FGF23, independent of demographics, laboratory values, peritoneal dialysis modality and adequacy, and treatment with vitamin D analogs and phosphate binders. Urinary and dialysate FGF23 clearances were minimal. In three serial monthly measurements, within-subject variability accounted for only 10% of total FGF23 variability compared with 50% for PTH and 60% for serum phosphate.

Conclusions: Increased serum phosphate, loss of residual renal function, longer dialysis vintage, and lower renal phosphate clearance are associated with elevated FGF23 levels in ESRD patients undergoing peritoneal dialysis. FGF23 may be a more stable marker of phosphate metabolism in ESRD than PTH or serum phosphate.

Figure 1.

Relationships between fibroblast growth factor 23 (FGF23) and residual renal function, dialysis vintage, serum phosphate, and phosphate clearance. Scatter plots depict the unadjusted associations of lnFGF23 with (A) serum phosphate; (B) residual renal function; (C) dialysis vintage; and (D) phosphate clearance. For each relationship, linear regression lines and Pearson correlation coefficients with their respective P values are shown.

Figure 2.

Range of variation in mineral metabolism markers. The plots depict mean (blue squares) and range of variation (green whiskers for lower and upper range values) in (A) fibroblast growth factor 23 (FGF23), (B) lnFGF23, (C) parathyroid hormone (PTH), (D) lnPTH, and (E) phosphate. Values for each individual participant are plotted in rank order of their individual means. In (A), the area shaded in light gray encompasses FGF23 values >15,000 RU/ml, and the area shaded in dark gray included FGF23 values >150,000 RU/ml.