What is the difference between single frequency bioimpedance analysis (SF-BIA), multi frequency BIA (MF-BIA) and bioimpedance spectroscopy (BIS)?
A. Most single frequency devices (SF-BIA) (and fat scales) measure only at 50 kHz and therefore measure impedance which is influenced by a combination of ECW and ICW. There are multi frequency devices (MF-BIA) that measure from 3 to 8 frequencies (between 5-800 kHz), but these devices allow also no accurate differentiation between ECW and ICW. MF-BIA uses empirical linear regression models to evaluate FFM, TBW, ICW and ECW that usually only apply to healthy subjects. Bioimpedance spectroscopy (BIS) uses physiological modeling and mixture equations (Cole–Cole plot and Hanai formulae) to first determine the electrical resistance of ECW and ICW and then calculate the volumes of these respective compartments. This is essential for identification of OH – the BCM – Body Composition Monitor uses the BIS technique.
