Abstract
Objective. To determine the level of agreement between measurements of body composition by air-displacement plethysmography (ADP) and bioelectrical impedance analysis (BIA) in obese/non-obese children and adolescents. Methods. Fat mass (FM) and fat free mass (FFM) were measured by ADP using the BOD-POD system and foot-to-foot BIA in 187 children and adolescents (75 males and 112 females, aged 5 to 22 years). Obesity was defined as a percentage FM (determined by BOD-POD), as a percentage (%) higher than 25%–35%. Sixty-four subjects were obese and 123 non-obese. Results. Lin's Concordance Coefficient (Rc) between estimates of FM (%) and FFM (kg) was 0.79 (95%CI: 0.73; 0.83) by BIA and 0.96 (95%CI: 0.95; 0.97) by ADP. For the group of patients as a whole, the mean difference (p < 0.001) between methods (the BIA measurement minus the ADP measurement) was −3.39 (95%CI: −4.13; −2.65) for FM (%) and 1.54 (95%CI: 1.10; 1.98) for FFM (kg) (p < 0.001). The limits of agreement were −13.70; 6.90 for FM (%) and 1.40; 7.60 for FFM (kg). In the obese group, the mean difference between methods was −5.01 (95%CI: −6.21; −3.81) for FM (%) and 2.58 (95%CI: 3.45; 1.71) for FFM (kg) (p < 0.001). In the non-obese group, these mean differences were 2.49 (95%CI: −3.41; −1.57) and 0.96 (95%CI: 1.43; 0.50), respectively (p < 0.001). Conclusions. Compared with ADP, foot-to-foot BIA overestimates FFM and underestimates FM in obese and non-obese children of either sex. ADP and BIA estimates of FFM and FM are highly correlated for both obese/non-obese children. However, the large limits of agreement suggest that these methods should not be used interchangeably.
We thank all the children and their families who participated in this study, and the nurses, dieticians and technicians for their expertise and assistance. This work was supported by a grant from the Navarra Government (Health Department).
CA was responsible for study design, anthropometry measurements, data collection, statistical analysis and writing of the manuscript. NK was responsible for data collection, statistical analysis and revision of the manuscript. GF was responsible for body composition measurements by BOD-POD system and revision of the manuscript.