Day-to-day variability of adequacy indexes in peritoneal dialysis

Background. The achievement of dialysis adequacy targets in peritoneal dial ysis (PD) is assessed by the calculation of the Kt/V and creatinine clearan ce (C-Cr) obtained by collecting dialysate and urine, usually two or three times a year. Prescription decisions are based on such adequacy assessments , regardless of any variability in the single measurements. The aim of our study was to assess the day-to-day variability of common dialysis adequacy parameters and to evaluate its impact on the adequacy indexes in PD. Methods. Twenty-four patients (14 CAPD, 10 APD) at two centres were studied by means of a triple dialysate and urine collection for a period of 1 week . Variability in the findings for a given patient was expressed by the coef ficient of variation (CV%) calculated for peritoneal (p), renal, and total (tot) adequacy parameters. The target Kt/V and C-Cr values were recalculate d on the basis of variability. Results. Kt/V was less variable (CV 4.0 and 4.4% for peritoneal Kt/V (pKt/V ) and total Kt/V (totKt/V) respectively) than C-Cr (4.7 and 6.0% for perito neal creatinine clearance (pC(Cr)) and total creatinine clearance (totC(Cr) ) respectively) and proved to be a more reliable indicator of adequacy in t erms of the CV. Both variability parameters became worse if renal clearance was added to peritoneal clearance. CV in APD proved to be no different fro m CAPD for all the parameters considered. In our centres dialysis adequacy target correction for variability provided safe values for weekly Kt/V (pKt /V=1.78-2.10 and totKt/V=1.82-2.15 target 1.7-2.0) and C-Cr/1.73 (pC(Cr)=53 .7-64.41 and totC(Cr)=55.1-66.11; target 50-601). Conclusions. Evaluating the adequacy of PD by means of a single measurement should take into account the weekly variability as demonstrated by a tripl e dialysate and urine collection. Standard adequacy targets can be correcte d to allow for variability. Thus one can obtain safe values for prescriptio n decisions based on a single collection result.