Evaluation of a new bioelectrical impedance instrument for the prediction of body cell mass independently of height or weight

The objective of the present study was to evaluate the performance of a new bioelectrical impedance instrument, the Soft Tissue Analyzer (STA), which predicts a subject's body composition. A cross-sectional population study i n which the impedance of 205 healthy adult subjects was measured using the STA. Extracellular water (ECW) volume (as a percentage of total body water, TBW) and fat-free mass (FFM) were predicted by both the STA and a compartm ental model, and compared according to correlation and limits of agreement analysis, with the equivalent data obtained by independent reference method s of measurement (TBW measured by D2O dilution, and FFM measured by dual-en ergy X-ray absorptiometry). There was a small (2.0 kg) but significant (P < 0.02) difference in mean FFM predicted by the STA, compared with the refer ence technique in the males, but not in the females (-0.4 kg) or in the com bined group (0.8 kg). Both methods were highly correlated. Similarly, small but significant differences for predicted mean ECW volume were observed. T he limits of agreement for FFM and ECW were -7.5-9.9 and -4.1-3.0 kg, respe ctively. Both FFM and ECW (as a percentage of TBW) are well predicted by th e STA on a population basis, but the magnitude of the limits of agreement w ith reference methods may preclude its usefulness for predicting body compo sition in an individual. In addition, the theoretical basis of an impedance method that does not include a measure of conductor length requires furthe r validation. (C) Elsevier Science Inc. 2000.