Best Method for Estimating Urea Volume of Distribution: Comparison of Single Pool Variable Volume Kinetic Modeling Measurements with Bioimpedance and Anthropometric Methods

The urea volume of distribution (Vurea) is a key component of the Kt/V parameter calculated during urea kinetic modeling. The Vurea parameter has been approximated empirically using total body water (TBW) estimates derived from anthropometric formulas or measured by bioelectric impedance analysis (BIA). The author compared TBW values derived using various anthropometric formulas (Watson, Hume, Randall, Tzamaloukas, Chertow) and BIA to the Vurea parameter calculated using three point variable volume single pool urea kinetic modeling. A total of 127 chronic hemodialysis patients were studied (mean age 66 ± 13 years; 42% female; 37% black; 47% diabetic). Agreement between anthropometric formulas, BIA, and Vurea values was assessed by linear regression and Bland Altman analyses. The closest correlations were obtained with the BIA (r = 0.972), Chertow (r = 0.917), and Tzamaloukas (r = 0.905) methods. When compared with Vurea, 95% confidence intervals by Bland Altman analysis were lowest with BIA (4L) and highest with the Watson method (8L). These results indicate that BIA best approximates Vurea in dialysis patients.