CREATININE CLEARANCE IN CONTINUOUS PERITONEAL-DIALYSIS - DIALYSIS DOSE REQUIRED FOR A MINIMAL ACCEPTABLE LEVEL

Objectives: To identify the most advantageous formula for estimating c reatinine clearance (CCr) and to establish a dose of dialysis that wil l ensure minimal acceptable levels of creatinine clearance in patients on continuous peritoneal dialysis (CPD). Design: Analysis of all CCr studies performed in CPD patients over 40 months. Setting: All four di alysis units following CPD patients in one city. One dialysis unit is government-owned, one is university-affiliated, and two are community- based. Participants: One hundred and ninety-four patients representing almost the entire CPD population in Albuquerque. Interventions: Creat inine and urea clearance studies were performed in 24-hour urine and d rained dialysate samples. Creatinine clearance (peritoneal plus urinar y) was normalized to either 1.73 m(2) body surface area (CCr) or body water estimated by the Watson formulas (KT/V-Cr). CCr and KT/V-Cr were either corrected by averaging urinary creatinine and urea clearances or were not corrected. Two dialysis units were designated as the train ing set (92 patients, 143 clearance studies) and the other two units a s the validation set (102 patients, 181 clearance studies). Main Outco me Measures: Minimal acceptable creatinine clearance levels were deter mined in the training set by computing the creatinine clearance value corresponding to 1.70 weekly KT/V urea by linear regression. Logistic regression models predicting low creatinine clearance were developed i n the training set and were tested in the validation set. Results: The following weekly creatinine clearance values corresponded to 1.70 KT/ V urea: corrected CCr 52.0 L/1.73 m(2), uncorrected CCR 54.4 L/1.73 m( 2), corrected KT/V-Cr 1.46, uncorrected KT/V-Cr 1.53. Logistic regress ion identified as predictors of low creatinine clearance low daily uri ne volume (UV) and low daily dialysate drain volume/body water (DV/V) for all four creatinine clearance formulas, plus low/low-average perit oneal solute transport (only for uncorrected CCr) and serum creatinine (for both KT/V-Cr formulas). In the validation set, the predictive mo dels produced an area under the receiver operating characteristic (ROC ) curve between 0.835 and 0.919 indicating very good predictive accura cy. For corrected CCr and anuria, the regression model produced a mini mal normalized drain volume (DV/V) value consistent with minimal accep table CCr equal to 0.305 L/L per 24 hours. This DV/V cutoff detected l ow corrected CCr in validation set anuric subjects (n = 55) with a sen sitivity of 85% and a specificity of 71%. For uncorrected CCr and anur ia, DV/V cutoffs were 0.273 L/L per 24 hours (high/high-average perito neal solute transport) and 0.420 L/L per 24 hours (low/low-average tra nsport). Sensitivity and specificity of these cutoffs in validation se t anuric subjects were 87% and 85%, plus 86% and 33%, respectively. Co nclusions: The uncorrected CCr appears to be the most advantageous cre atinine clearance formula in CPD, because it allows the use of periton eal solute transport type in the calculation of the minimal required n ormalized drain volume. The minimal acceptable uncorrected CCr is 54.4 L/1.73 m(2) weekly. To achieve this uncorrected CCr in anuria, the re quired minimal normalized drain volume is 0.273 L per liter of body wa ter daily if peritoneal solute transport is high or high-average and a round 0.420 L per liter of body water daily if peritoneal solute trans port is low or low-average. The required total daily drain volume is c omputed by multiplying the required normalized drain volume by body wa ter.