Estimation of total body water by bioelectrical impedance analysis

Total body water (TBW) measured by bioelectrical impedance analysis (BIA) was directly compared with deuterium-isotope dilution in a total of 58 subjects. First, sex-specific and group equations were developed by multiple regression analysis in (10 each) obese and nonobese men and women. Height²/resistive impedance was the most significant variable used to predict deuterium-dilution space (D₂O-TBW) and, combined with weight, yielded R = 0.99 and SE of estimate = 1.75 L. Equations predicted D₂O-TBW equally well for obese and nonobese subjects. Second, the equations were prospectively tested in a heterogenous group of 6 males and 12 females. Sex-specific equations predicted D₂O-TBW with good correlation coefficients (0.96 and 0.93), total error (2.34 and 2.89 L), and a small difference between mean predicted and measured D₂O-TBW (-1.4 ± 2.05 and -0.48 ± 2.83 L). BIA predicts D₂O-TBW more accurately than weight, height, and/or age. A larger population is required to validate the applicability of our equations.