Multi-frequency bioelectrical impedance for the prediction of body water compartments: validation in different ethnic groups.

Body weight, body height and impedance at 1 kHz and at 100 kHz were measured in the fasting state in groups of healthy adult males and females from Ethiopia, China, Italy and The Netherlands. Total body water (TBW) and extracellular water (ECW) were determined by deuterium oxide and bromide dilution respectively. TBW/height and ECW/height were calculated as a measure of body build. The relation between TBW and ECW as measured by dilution technique and impedance index (height2/impedance) at 100 kHz and 1 kHz respectively was not different between the four populations. When a prediction formula for TBW and ECW from impedance index, developed in another (Dutch) population was applied to the four country groups, TBW was slightly overestimated, varying from 0.1 ± 1.8kg in the Italian group to 0.6 ± 1.8kg in the Dutch group. Also ECW was slightly but significantly overestimated, varying from 0.3 ± 0.9kg in the Dutch group to 1.1 ± 0.9kg in the Italian group. The bias for TBW was correlated with TBW/height in all country groups (correlation coefficients ranging from 0.33 to 0.56, all p<0.05) and the bias for ECW was correlated with ECW/height in all country groups (correlation coefficients ranging from 0.52 to 0.63, all p<0.05) except in the Ethiopians (r=0.23, p<0.1). Moreover, the bias for TBW and ECW was, in two of the four country groups, correlated with body water distribution (ECW/TBW). When the differences between measur 1000 ed and predicted TBW and ECW were corrected for differences in TBW/height and ECW/height and for differences in body water distribution, the bias significantly decreased and was not different from zero any more. It is concluded that multi-frequency bioelectrical impedance is an appropriate technique to predict body water compartments in populations. Difference between (ethnic) groups can be partly attributed to differences in body build.