Body water compartment measurements: A comparison of bioelectrical impedance analysis with tritium and sodium bromide dilution techniques

Background and Aims: This study was undertaken to assess the comparability of body water compartment estimates in healthy volunteers using single and dual frequency bioelectrical impedance analysis (BIA) with established refe rence methods of tritium and NaBr dilution. Methods: Total body water (TBW) was estimated in 10 healthy volunteers using single frequency (50 kHz) BIA (Bodystat 1500), dual frequency (5 and 200 kHz) BIA (Bodystat Dualscan 200 5) and tritium dilution. Extracellular water (ECW) was measured with dual f requency BIA and NaBr dilution. BIA was performed using distal tetrapolar e lectrodes in the supine position. Venous blood was sampled for measurement of background concentrations of tritium and NaBr using a beta counter and h igh performance liquid chromatography respectively. 10 ml tritiated water ( 3.7 MBq) and 50 ml 5% Na Br solution were then injected intravenously and b lood samples taken from the opposite arm every 45 min for 4.5 h for estimat ion of concentrations of tritium and Na Br. Results: There was good correla tion (r(2) = 0.76) between estimates of ECW using dual frequency BIA and Na Br dilution, with the former overestimating ECW by similar to1 L. However, this difference varied systematically with body weight. Although TBW measu rements obtained by single and dual frequency BIA correlated well with esti mates using tritium dilution (r(2) = 0.96 and 0.95 respectively), single fr equency BIA underestimated TBW by similar to1 L and dual frequency BIA by s imilar to 5 L compared to tritium dilution. Conclusion: TBW measurements ob tained using the single frequency BIA device were more accurate than those obtained using the dual frequency BIA device. Dual frequency BIA provided a reasonably accurate estimate of ECW. (C) 2001 Harcourt Publishers Ltd.