Is Total Creatinine Clearance a Good Predictor of Clinical Outcomes in Continuous Ambulatory Peritoneal Dialysis?

The measurement of the adequacy of dialysis in continuous ambulatory peritoneal dialysis (CAPD) is controversial. The use of weekly total creatinine clearance (TCC) has been recommended, but not validated. We analyzed data from our recent urea kinetics in a CAPD study to investigate TCC and its relationship to patient outcomes. TCC was measured over 24 hours by adding residual renal and peritoneal creatinine clearance, correcting for 1.73 m2 surface area and converting to a weekly value. Seventy-six patients had 218 measurements, on starting CAPD and then at 6–month intervals, with mean follow-up of 20 months (range 1–57 months). The mean TCC was 73.62±32.11 L/week. Due mainly to the loss of residual renal function, the TCC decreased with time (r=-0.40, p<0.0001), from 88.65 L/week initially to 66.11 at one year, 59.84 at two years, and 50.47 at three years. Dialysate-to-plasma creatinine concentration ratios (DIP Cr) increased with time (r=0.28, p<0.0001) from 0.62 initially to 0.66 at one year and 0.73 at two years. The TCC correlated significantly with serum levels of creatinine (r=-0.46, p<0.0001), urea (r=-0.21, p<0.001), potassium (r=-0.14, p<0.05), phosphate (r=-0.25, p<0.001), and hemoglobin (r=0.16, p<0.01), but not with serum albumin or with clinical outcomes including technique failure, hospital days, transfusions, peritonitis rate, nerve conduction velocity, or subjective indices of well-being, except for a weak correlation with the fatigue index (r=0.19, p<0.05). However, of 13 deaths 6 occurred in patients with TCC under 48 L/week (p<0.05). There is little evidence of a proportionality relationship between TCC and clinical outcomes in CAPD, but a TCC of 48 L/week may usefully define a lower limit below which excess mortality occurs.