HUMAN HYDROMETRY - COMPARISON OF MULTIFREQUENCY BIOELECTRICAL-IMPEDANCE WITH (H2O)-H-2 AND BROMINE DILUTION

The traditional method of assessing total body water (TBW), extracellu lar water (ECW), and intracellular water (ICW) has been the use of iso topes, on the basis of the dilution principle. Although the developmen t of bioelectrical impedance techniques has eliminated many of the mea surement constraints associated with the dilution methods, the degree of interchangeability between the two methods remains uncertain. We us ed multifrequency bioelectrical impedance spectroscopy (BIS), (H2O)-H- 2 dilution, and bromine dilution to assess TBW, ECW and ICW in 469 hea lthy subjects (248 males, 221 females) aged 3-29 yr. We found that the TBW, ECW and ICW estimates for the BIS and dilution methods were sign ificantly correlated (r(2) = 0.80-0.96, P < 0.0001, SE of the estimate = 2.3-2.7 liters). On the basis of population, the constants used in the BIS analysis could be adjusted so that the mean differences with t he dilution methods would become zero. The SD values for the mean diff erences between the dilution and BIS methods, however, remained signif icant for both males and females: TBW(+/-2.1-2.8 liters), ECW (+/-1.4- 1.6 Liters), and ICW (2.0-3.1 liters). To improve the accuracy of the BIS measurement for an individual within the age range we have examine d, further refinement of the constants used in the BIS analysis is nee ded.