Phosphorus metabolism in peritoneal dialysis- and haemodialysis-treated patients

Abstract

Background: Phosphorus control is generally considered to be better in peritoneal dialysis (PD) patients as compared with haemodialysis (HD) patients. Predialysis phosphorus concentrations are misleading as a measure of phosphorus exposure in HD, as these neglect significant dialysis-related fluctuations.

Methods: Parameters of mineral metabolism, including parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF-23), were determined in 79 HD and 61 PD patients. In PD, phosphorus levels were determined mid-morning. In HD, time-averaged phosphorus concentrations were modelled from measurements before and after the mid-week dialysis session. Weekly renal, dialytic and total phosphorus clearances as well as total mass removal were calculated from urine and dialysate collections.

Results: Time-averaged serum phosphorus concentrations in HD (3.5 ± 1.0 mg/dL) were significantly lower than the mid-morning concentrations in PD (5.0 ± 1.4 mg/dL, P < 0.0001). In contrast, predialysis phosphorus concentrations (4.6 ± 1.4 mg/dL) were not different from PD. PTH and FGF-23 levels were significantly higher in PD. Despite higher residual renal function, total phosphorus clearance was significantly lower in PD (P < 0.0001). Total phosphorus mass removal, conversely, was significantly higher in PD (P < 0.05).

Conclusions: Our data suggest that the time-averaged phosphorus concentrations in patients treated with PD are higher as compared with patients treated with HD. Despite a better preserved renal function, total phosphorus clearance is lower in patients treated with PD. Additional studies are needed to confirm these findings in a population with a different demographic profile and dietary background and to define clinical implications.

Keywords: CKD-MBD; FGF-23; dialysis; hyperphosphataemia; mineral metabolism.