Time profiles of peritoneal and renal clearances of different uremic solutes in incident peritoneal dialysis patients

Background: Residual renal function (RRF) contributes substantially to the adequacy of peritoneal dialysis (PD). In the presence of RRF, maintenance of an adequate fluid balance is facilitated, level of systemic inflammation is lower, and renal endocrine functions are preserved. The beneficial impact of RRF also may be related to the preservation of specific renal elimination mechanisms, such as tubular metabolism or secretion, which are crucial for the removal of some uremic retention solutes. Methods: Time profiles of peritoneal and renal clearances of urea nitrogen (60 d), creatinine (113 d), phosphate (96 d), the middle molecule beta(2)-microglobulin (beta M-2; 11.8 kd), and the protein-bound solute p-cresol (108 d) were investigated prospectively in 24 incident PD patients. Data were analyzed by using the linear mixed models procedure. Results: During a median follow-up of 7.2 months (range, 5.6 to 8.6 months), RRF (P = 0.001) and 24-hour urine volume (P = 0.004) declined significantly. Twenty-four-hour peritoneal drainage volume increased (P < 0.0001). Renal clearances of urea nitrogen (P = 0.0002), creatinine (P = 0.001), and phosphate (P = 0.001) decreased. Peritoneal clearances of these solutes increased (P = 0.002, P < 0.0001, and P < 0.0001, respectively). There was a decline in renal clearances of beta M-2 (P = 0.0004) and p-cresol (P < 0.0001). No change in peritoneal clearances of these solutes was noted (P = 0.188 and P = 0.559, respectively). Conclusion: Increasing PD dose may compensate for deteriorating RRF with respect to the elimination of water-soluble solutes. This is not the case for the middle molecule beta M-2 and the protein-bound solute p-cresol.