Assessment of Dialysis Dose by Measured Clearance versus Extrapolated Data

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Abstract
Objective: To determine whether estimates of daily dialysis clearance of creatinine and urea, based on data from the 4-hour peritoneal equilibration test, correlate well with daily dialysis clearance measured by 24-hour dialysate collection in chronic ambulatory peritoneal dialysis patients. Design: Prospective study in which each subject collected all dialysate from a 24-hour period and then immediately thereafter underwent a standard peritoneal equilibration test (PET). Daily clearances of creatinine and urea were calculated from 24-hour dialysate collections by standard methods and then were compared with several estimates of 24-hour clearance based on PET data. Setting: Single peritoneal dialysis unit of a university teaching hospital. Patients: Thirty-six stable patients on continuous ambulatory peritoneal dialysis (CAPD). Main Outcome: The estimated values for daily dialysis clearance both overestimated and underestimated the measured 24-hour clearance. The correlation coefficient between the extrapolations and the actual 24-hour clearances ranged from 0.63–0.68. The range of discordance for daily creatinine clearance was from -2530 mL/dayto +2199 mL/day. For daily urea clearance, the range of discordance was from -21 03 mL/ day to +1940 mL/day. The peritoneal membrane transport characteristics of the individual patient did not predict whether the extrapolation overestimated orunder estimated the measured daily clearance. Conclusion: Extrapolation of PET data is not a reliable method to estimate the dose of dialysis delivered to the patient. A 24-hour collection of dialysis is necessary for this determination.