Reproducibility of studies of peritoneal dialysis adequacy

To assess the variability and reproducibility of dialysis adequacy clearance measurements (weekly Kt/V and weekly creatinine clearance/1.73 m2 BSA) in a given patient, 42 patients underwent three clearance studies in a one week period. The dialysis prescription was kept constant. There were 21 males with a group mean age of 49 +/- 15 years; 37 patients performed CAPD and 5 DAPD; the dialysis prescription was 6 to 12 liters/day; and 17 patients were anuric. To assess test variability within each patient, the coefficient of variation (CV) and the range were determined for each patient's three clearance values, and for the factors that determine those values. These were averaged to determine the mean patient variability (CV and range) of those measurements. The mean patient CV of the weekly Kt/V was 8.1%. The mean patient range of the weekly Kt/V was 0.30. Of the determinants of total Kt/V, the greatest variability (GV) existed in residual renal urea clearance at 35.4%, with moderate variability seen for peritoneal dialysis urea clearance at 7.0%, which was more a function of variability in D/P urea (CV = 6.3%) than variability in drain volume (CV = 4.1%). There was little variability in V (CV = 0.6%). Similar results were seen for the variability in weekly creatinine clearance measurements. We found that the day-to-day reproducibility of Kt/V measurements is limited, especially in patients with residual renal function, although day-to-day variability in D/P urea also affects Kt/V reproducibility in all patients. Values that fall into the borderline "adequate" range may need to be repeated when considering a patient's dialysis prescription. In addition, research that involves the measurement of Kt/V should utilize more than one collection to increase the reliability of those measurements.