HDCN Article Review/Hyperlink

Rodby RA, Firanek CA, Cheng YG, Korbet SM

Reproducibility of studies of peritoneal dialysis adequacy

Kidney Int (Jul) 50:267-271 1996

In this simple, but excellent and important study, Rodby et al from Korbet's group in Chicago, studied the reproducibility of 24 hour dialysate and urinary collections for calculation of Kt/V and creatinine clearance in 61 CAPD and 7 DAPD patients. Three data collections were done in one week by each patient and co-efficients of variation were calculated. It is suggested that co-efficients greater than 6% are clinically significant. The results show that the co- efficients of variation for Kt/V and creatinine clearance were 8.1 and 9.4% respectively. Most notable was that the residual renal urea and creatinine clearances had co-efficients of 35 and 30% respectively. Peritoneal urea and creatinine clearances varied less with co-efficients of 7.0 and 7.4% respectively. A significant variation was also seen in D/P urea [6.3% co- efficient] and D/P creatinine [6.8% co-efficient].

Comment: These variations are clinically important, and in the case of Kt/V, are equivalent to a range of 0.30 per week. The CANUSA study would suggest that a 0.3 difference in weekly Kt/V corresponds to a 15% difference in mortality. The conclusion is that a single 24 hour collection of dialysate and urine may not be sufficient. If in doubt, the test should be repeated. There is a case to be made for doing all the measurements in duplicate but this would be logistically difficult. Certainly, this study makes a case for doing 48 hour rather than 24 hour urine collections. One wonders if the co-efficient of variation would be less if the investigators had excluded all patients with urine volumes less 100 ml/day, as is the practice in many Units when they do their collections. Large variations in equilibration ratios for urea and creatinine are a little surprising. One wonders if this reflects variable dwell times from day-to-day which can occur even in patients with a constant prescription. It also may be affected by variations in residual volumes of dialysate. The authors are to be congratulated for opening up this whole subject for debate. (Peter G. Blake, M.D., Victoria Hospital, London, Ontario)