Superior dialytic clearance of β2-microglobulin and p-cresol by high-flux hemodialysis as compared to peritoneal dialysis

Both residual renal and dialytic clearance confer to the total solute clearance in dialysis patients. Dialytic clearances of the middle molecule beta-microglobulin (beta M-2) and the protein-bound solute p-cresol (pcr) are generally believed to be higher with peritoneal dialysis (PD) as compared to hemodialysis (HD). Supportive data, however, are lacking. We performed a single-center cross-sectional observational study including 70 unselected patients treated with either high-flux HD (n = 20) or PD (n = 50). Mid-day serum levels (PD) and time- averaged concentrations ( HD) of the water-soluble solutes urea nitrogen, creatinine and phosphate, the middle molecule beta M-2, and the protein- bound solute pcr were determined. Dialytic solute clearances (l/week/1.73 m(2)) were calculated from total dialysate collection during the mid-week session in HD and 24 h dialysate collection in PD. Renal clearances were calculated for each of the respective solutes from a timed urine collection. Total clearances were obtained by summation. HD delivered significantly higher clearances of all retention solutes studied. This superiority was especially pronounced for pcr (30.9 +/- 62.7 vs 4.4 +/- 2.3, HD vs PD, P < 0.0001) and b2M (28.6 +/- 6.6 vs 5.8 +/- 3.1, HD vs PD, P < 0.0001). Renal clearances, conversely, were significantly higher in patients on PD. Serum levels of all solutes but pcr were significantly lower in HD than in PD. Both a higher residual renal function and a lower generation rate contribute to the lower pcr levels in PD. In conclusion, superior dialytic clearance of both water-soluble solutes, beta M-2, and pcr is achieved by high-flux HD as compared to PD.