A comparison of four commercial systems used to measure whole-body electrical impedance.

Four commercial whole-body impedance measuring systems (Holtain, RJL, Bodystat and EZcomp) were compared on two separate occasions for a group of normal subjects. The first set of readings in 21 subjects demonstrated a significant difference of approximately 6% between the Holtain measurement and the higher readings from the Bodystat or RJL systems. The differences between the RJL and Bodystat readings were much less (mean difference 0.6%). Similar differences between the Holtain and EZcomp or Bodystat measurements were demonstrated on a second occasion for a group of 11 subjects. Given that these devices operate by supplying a constant current, the differences may be explained by the results from a series of measurements on a whole-body resistance simulator in which it appears that for skin contact resistance > 200 omega the Holtain device is unable to sustain a constant current and therefore records a lower impedance than the true value.