Patients on conventional hemodialysis lose residual renal function more rapidly than patients on continuous ambulatory peritoneal dialysis (CAPD). The effect of dialysis using synthetic membranes and ultrapure water is less clear. The decline of urea clearance was compared in a cohort of 475 incident end-stage renal failure patients who received treatment with CAPD (N=175) or hemodialysis (HD) utilizing high-flux polysulphone membranes, ultrapure water, and bicarbonate as the buffer (N=300). CAPD patients were significantly younger, fitter (lower comorbidity severity score), less dependent (higher Karnofsky performance score) and less likely to have presented late than HD patients. There was no difference in the mean urea clearance in each group at dialysis initiation, or at any 6-month time point during the ensuing 48 months. This was true even after exclusion of patients who had died in the first year after initiation, those transferred to another dialysis modality, or those who had been transplanted. Only age and chronic interstitial disease predicted retention of urea clearance at one year. The rate of decline of urea clearance was similar in pre- and post-dialysis initiation phases, though there may have been a step-decline of about 2 mL/min at initiation, which requires further investigation. In hemodialysis using high-flux biocompatible membranes and ultrapure water, residual renal function declines at a rate indistinguishable from that in CAPD. This may have important implications, since preservation of residual renal function has major benefits and is a valid therapeutic goal.
