RESUMEN
Objective: To evaluate the consistency between bioelectrical impedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA) in the measurement of body composition in children and adolescents aged 7-17 years. Methods: Fat-free mass (FFM) and fat mass (FM) were measured by both BIA and DXA in 1 431 children. The consistency between the methods was evaluated by intra-class correlation coefficients (ICCs) and Bland-Altman analysis. Logarithmic transformation of both measurements was performed before Bland-Altman analysis. Results: The ICCs for FFM were 0.986 and 0.974 and ICCs for FM were 0.854 and 0.926 in boys and girls respectively. In boys, the mean ratio of FFMs by BIA and DXA was 1.04, with limits of Agreement (LoA) of 0.95-1.14, and in girls, the mean ratio of FFMs by BIA and DXA was 1.02, with the LoA of 0.90-1.15. The LoA of FFM became narrower with age in both boys and girls. Both boys and girls had the wide LoAs for FM (0.40-1.27 and 0.48-1.48, respectively). Additionally, the LoA ranges for FFM and FM narrowed with the increase of BMI level in both boys and girls. Conclusion: For all children, BIA showed good consistency with DXA for FFM, whereas significant errors occurred in FM measurement. The consistency between BIA and DXA was better for obese children than for underweight or normal-weight children.
