Hydration status assessed by multi-frequency bioimpedance analysis

Hydration status in human subjects can be assessed by multifrequency bioimpedance analysis (MFBIA) which uses the higher conductivity of water to determine its volume. From the resistance values at low and high frequencies, the extracellular water (ECW) and the total body water (TBW) are derived, respectively. Intracellular water (ICW) is then derived from the values of TBW and ECW. Standard MFBIA equations completely failed to predict changes in ECW and TBW during short term 2-3% dehydration and rehydration of three male subjects. Electrolyte concentration and water distribution may determine tissue conductivity as much as water volume per se.