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Article Review/Hyperlink
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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)
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