The method used for volume estimation significantly influences KprT/V results in peritoneal dialysis patients

We studied 51 patients (age 50 +/- 15 years; weight 75 +/- 17 kg; blood urea nitrogen 62 +/- 20 mg/dL), 61% of whom were obese. The volume of distribution of urea was estimated by anthropometric formulas (Watson and Hume) and as 58% of actual and ideal body weight. Volumes derived from use of 58% of actual body weight were highest (43.4 +/- 10.0 kg; p = 0.0005); no differences were noted between Watson and Hume volumes and those obtained using 58% of ideal body weight (38.5 +/- 8.0, 39.4 +/- 7.5, and 37.0 +/- 5.6 kg, respectively). Normalized daily urea clearance (KprT/V) was lowest and highest when using 58% of actual and ideal body weight, respectively (0.251 +/- 0.081 and 0.290 +/- 0.091; p < 0.0001). KprT/V values derived using the Watson and Hume methods were similar (0.279 +/- 0.081 and 0.274 +/- 0.083, respectively), but significantly lower than those obtained using actual body weight (p < 0.0001). Differences were magnified in obese patients. A subset of patients underwent hemodialysis for urea volume measurement by urea kinetic modeling. Volume estimates using bioelectrical impedance showed the least bias when compared to values calculated during a hemodialysis treatment. We conclude that KprT/V is very dependent on body habitus and the method used for volume determination. Standardization of the volume parameter is essential to defining therapeutic guidelines and for meaningful comparisons between centers.