Validation of leg-to-leg bio-impedance analysis for assessing body composition in obese Chinese children

This study was designed to validate the Tanita (TBF_401) leg-to-leg bio-impedance analysis (BIA) system by comparing with dual-energy X-ray absorptiometry (DXA) in assessing the body composition in Chinese obese children. Free fat mass (FFM), fat mass (FM) and percentage body fat (%BF) were measured with BIA and DXA in 64 children (44 males, 20 females) with group mean BMI of 29.9 ± 5.0 kg/m². In all subjects, estimates of FFM, FM and %BF were highly correlated (r =0.85-0.95, P <0.001) between the two methods and the correlations were not gender dependent. However, a Bland-Altman comparison showed wide limits of agreement between the methods and the results of the comparisons were also not gender dependent. The mean difference in FFM, FM and %BF between BIA and DXA was -0.82 kg, -0.52 kg and -0.34% while the limits of agreement were -8.64 to 6.99 kg, -8.47 to 7.43 kg and -11.19 to 10.50%, respectively. Moreover, positive correlation was found between the mean and differences (BIA vs DXA) in FM (r =0.55, P <0.001) and %BF (r =0.73, P <0.001). The aforementioned findings showed that the leg-to-leg BIA system is a valid instrument to assess body composition in both genders of obese Chinese children. Nevertheless, by comparing with DXA, the leg-to-leg BIA might overestimate the FM and %BF in serious obese children. Moreover, the large limits of agreement between the BIA and DXA derived from Bland-Altman comparisons suggested that the two methods should not be used interchangeably.