OBJECTIVE: To determine the precision and bias of single- and multiple-frequency bioimpedance estimates of total body water (TBW) and extracellular water (ECW) volumes in comparison with the true values for these volumes established by gold standard dilution techniques. DESIGN: Controlled, prospective, open-label investigation. SETTING: Private, not-for-profit university-affiliated, acute care hospital. PARTICIPANTS: Normal, healthy men (n=8) and women (n=6) volunteers, 25–46 years of age. INTERVENTIONS: A single oral dose of a mixture of deuterium oxide 10 g and bromine 30 mmol; bioimpedance analysis pre- and three hours postrnixture administration. MAIN OUTCOME PARAMETERS: TBW and ECW volumes established by deuterium oxide and bromine dilutional spaces (gold standards), respectively, and single- and multiple-frequency bioimpedance estimates of those same volumes. RESULTS: The mean multiple-frequency bioimpedance (MFB) and single frequency bioimpedance (SFB) estimates of TBW, 41.2 and 42.1 L, respectively, were not statistically different (NS) from the 41.2 L deuterium oxide value. Although the two methods had similar precision (NS), MFB was less biased. For ECW, the mean MFB and SFB values of 19.5 and 24.8 L, respectively, were significantly different from the bromine value of 18.8 L (p=0.013 and p=0.001, respectively). MFB was the more precise and less biased predictor of ECW. CONCLUSIONS: Compared with SFB, the MFB approach is a more precise and less biased predictor of TBW and ECW volumes in young, healthy adults, and may offer more accurate assessment in subjects with aberrant physiology.
