Objective: To assess the nature of the decline in residual renal function (RRF) after the initiation of peritoneal dialysis, and to identify risk factors influencing the preservation of RRF. Design: A retrospective single-center study. Setting: Tertiary medical center. Patients: Eighty patients who were clinically stable and had been on continuous ambulatory peritoneal dialysis (CAPD) for a minimum of 6 months. Main Outcome Measures: All subjects had at least three measurements of RRF, which was calculated as the average of creatinine clearance (C(cr)) and urea clearance from a 24-hour urine collection. All measurements of RRF were plotted on a logarithmic scale and a linear scale against the duration of CAPD. Covariables used in the correlation analyses were age, sex, the presence of diabetes mellitus, mean blood pressure, mean diastolic blood pressure, hematocrit and C(cr) at the start of peritoneal dialysis, peritoneal membrane transport characteristics by peritoneal equilibration test (PET), and the rate of peritonitis. Results: A significant correlation was found between CAPD duration and RRF decline represented on a logarithmic scale with a correlation coefficient (r) of 0.355 (p < 0.001). In contrast, on a linear scale, the correlation coefficient was only 0.273 (p < 0.01). By linear multiple regression analysis, the only independent risk factor for the decline of RRF was the rate of peritonitis (r = -0.446, p < 0.001). Conclusion: These results suggest that RRF declines exponentially rather than linearly with time, and that the rate of peritonitis is an independent risk factor for the decline of RRF in CAPD patients.
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