A critical analysis of whole body bioimpedance spectroscopy (BIS) for the estimation of body compartments in health and disease

Aim of the study was to assess the accuracy and precision of a BIS device and the relative contribution of BIS beyond the anthropometric parameters. The output of the Impedimed device (SFB7) and the relative contribution of height, weight, age, sex and resistance values at zero and infinite frequency (Rzero and Rinf respectively) to the prediction of total body water (TBWd, deuterium space), of extracellular fluid (ECFbr, sodium bromide space) and of fat mass (FMDXA) were assessed in 116 subjects (32 healthy subjects and 84 patients with disorders of body composition). Using a repeated randomization procedure, new equations for TBW, ECF and FM were derived.The SFB7 gave measures of determination similar to those obtained with equations that included only anthropometric data. The SFB7, but not the newly derived regression equations, underestimated TBW and ECF by 3.82 ± 3.37 (mean ± SD) and by 0.93 ± 2.62 l and overestimated FM by 6.55 ± 3.86 kg. Nine of 16 patients with ECF overload as detected by ECFbr were also detected by BIS. BIS measurements contribute marginally but not significantly beyond anthropometric data to the prediction of TBW, ECF and FM, either in healthy subjects or in patients with disturbed body composition.