Total body water measurement: using the multifrequency BIS-Hanai approach with 50 kHz single frequency

In bioimpedance analysis (BIA), total body water volumes (TBW) are generally estimated from empirical correlations of the subject weight and his impedance index (H2/R50) where H denotes the subject height and R50 is his wrist-ankle resistance at 50 kHz. We have proposed recently [4] a modification of bioimpedance spectroscopy (BIS) for measuring directly TBW (Vtnm) from R∞, the wrist-ankle resistance extrapolated at infinite frequency and a mean TBW resistivity ρ∞ inferred from dual energy X-ray absorptiometry (DXA) measurements in 58 healthy subjects, using Hanai’s theory to account for non conducting elements. In this paper we investigate whether our new method could also be applied to single frequency bioimpedance at 50 kHz by using an appropriate 50 kHz resistivity. We have compared TBW volumes (Vt50) given by this method with our modified BIS method with BIA correlations from the literature and the classical BIS method using TBW deducted from fat-free mass measured by DXA (Vtd) assuming a hydration rate of 73.2% as reference. A validation of our methods was made using a 2nd set of data for 21 subjects not used for the determination of resistivities.