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 (Y-urea) is a key component of the Kt/V parameter calculated during urea kinetic modeling. The V-urea 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 V-urea 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 V-urea 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 V-urea, 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 V-urea in dialysis patients. ASAIO journal 2004; 50:237241.