[Clearances in automated intermittent peritoneal techniques: a new formula to use morning blood sampling]

According to the main guidelines, dialysis adequacy monitoring is fundamental in the management of patients on peritoneal dialysis. In order to avoid mistakes in the calculation of the peritoneal urea and creatinine clearance in patients on dialysis with intermittent techniques, the collection of blood samples about 6 hours after the end of the dialysis session is advised. In fact, because the creatinine and urea values at the end of dialysis (the morning values in NIPD) are the lowest, the resulting clearances could be overestimated. The mean values between the start and the end of the dialysis session are considered the gold standard. However, collecting a blood sample at 2.00 p.m. may be difficult and uncomfortable both for the nurse and the patient. In this paper we present two formulas (the first for urea and the second for creatinine) which, starting from the values at the end of dialysis, predict the values at the beginning of the session and consequently the mean values. The aim of this study was to validate the formulas by evaluating their capability to predict the mean urea and creatinine values when only end-of-dialysis blood sampling was performed. Statistical analysis was carried out using the Bland-Altman test. The two formulas proved able to predict the mean urea and creatinine values; the differences between the measured and calculated values were not statistically significant.