Inserm/AP-HP CIC 9202; Antenne RePOP-IdF, Hôpital Robert Debré, Paris , France; Bodystat Ltd, Isle of Man, UK.
Translation from French:
INTRODUCTION: The single frequency (50 kHz) bioelectrical impedance analysis (BIA) technology is a non-invasive, simple and quick technique for estimating Lean Body Mass (LBM) and Fat Mass (FM). Multi-frequency BIA allows, in addition, the estimation of intra and extra-cellular water because at a low frequency the current is unable to penetrate the body cell membrane whereas at a high frequency the current is able to penetrate the entire membrane. The multi-frequency unit Bodystat® Quadscan 4000 delivers only a measure of impedance (Z in Ω) at four frequencies and not a resistance (R in Ω) nor a reactance (Xc in Ω) used in most of the equations convenient for children.
Recently, the manufacturer of that unit has made available a Bodystat® Phase Angle software program enabling the calculation of the resistance and the reactance from the four impedance values.
PURPOSE OF THE STUDY: Purpose of the present work is to compare the values given by the two units for R and Xc at 50 kHz.
METHOD: The same day, without removing the electrodes, we made measurements with two units:
The Lean Body Mass was calculated using the HoutKooper equation (1)
Comparison was made between methods using bias (mean difference) and 95% limits of agreement (bias +/- 2SD) according to Bland & Altman (2). The significance of any differences between methods were tested by paired t-test.
RESULTS: The study was performed on 182 children in various age groups (age < 8 yrs:n= 42, age <12 yrs: n= 49, age < 16 yrs: n = 24, age > 16 yrs: n = 67).
CONCLUSION: The difference in the lean body mass measured by the two machines is not clinically significant; nevertheless it is recommended to use always the same machine for a longitudinal follow-up of subjects. The multi-frequency impedance technology allows an estimate of the intra and extra-cellular fluid compartments. The ratio Z5/Z200 could be an index of the fluid compartment distribution, independant of any regression equation. The measurement values determined by multi-frequency impedance remain indicative and need to be validated in this population.