Measurement of body water by multifrequency bioelectrical impedance spectroscopy in a multiethnic pediatric population

Background: Bioelectrical impedance spectroscopy (BIS) may provide a noninv asive, rapid method for the assessment of total body water (TBW), extracell ular water (ECW), and intracellular water (ICW). Few studies, however, have examined the accuracy of BIS in pediatric populations. Objective: Our objective was to evaluate the accuracy of BIS for the measur ement of TEW, ECW, and ICW in healthy children. Design: Dual-energy X-ray absorptiometry (DXA), total body potassium (TBK), and BIS measurements were performed in 347 children (202 males and 145 fem ales aged 4-18 y). The reference values for TEW, ECW, and ICW were defined by using a DXA+TBK model. BIS values were evaluated by using the method of Bland and Altman. A randomly selected calibration group (n = 231) was used to derive new BIS constants that were tested in the remaining group (n = 11 6). Results: BIS values were highly correlated with the reference values (r(2) = 0.94-0.97, P < 0.0001), but differences between the BIS and DXA+TBK model s for individuals were significant (P < 0.001). Use of new BIS constants re duced the mean differences between the BIS and DXA+TBK models; the SDs of t he mean differences were improved (1.8 L for TEW, 1.4 L for ICW, and 1.0 L for ECW) for the total population. Conclusions: On a population basis, BIS can be calibrated to replace the DX A+TBK model for the assessment of TEW, ECW, and ICW in healthy children. Th e accuracy of the BIS measurement in individual children may be refined fur ther by using age-and sex-specific adjustments for the BIS calibration cons tants.