ABSTRACT
Purpose: The aim of this study was to investigate the validity of bioelectrical impedance analysis (BIA) and air-displacement plethysmography (ADP) in relation to dual energy X-ray absorptiometry (DXA) (i.e. the reference standard). Methods: Sixty-three older adults aged 60-96 years (40 men, 23 women). Body percent fat (%BF) was estimated by BIA, ADP and DXA. Single frequency (50Hz) BIA that measures whole body impedance was used and Kyle\u27s equation was applied to estimate fat-free mass. Paired sample t-test, absolute percent errors and Cohen\u27s d were used to evaluate differences among the 3 different methods. Methods agreement was assessed by Pearson\u27s correlation, regression analysis and Bland-Altman plots. Classification agreement of obesity was evaluated using Kappa statistics. Results: ADP and BIA significantly overestimated %BF relative to DXA by 3.3% and 3.1%, yielding absolute errors of 14.1% and 12.4%, respectively. However, ADP (Cohen\u27s d=0.35) had better agreement with DXA and BIA (Cohen\u27s d=0.40). Regression analysis indicated smaller individual variations of ADP (SEE=3.23) compared to BIA (SEE=4.78). In addition, ADP (Kappa=0.58) showed better obesity classification agreement relative to DXA in comparison with BIA (Kappa = 0.35). However, Bland-Altman plots showed a positive proportional pattern (Slope= 0.24, R2=0.24, p\u3c0.05) of biases in ADP, while no systematic pattern of biases was observed for BIA. A gender difference was also detected, indicating a better agreement in males than females. Conclusion: Given that both BIA and ADP had acceptable agreement with DXA in estimating %BF of older adults, ADP showed relatively better agreement in body composition measurement (i.e. %BF) and obesity classification in comparison to BIA. However, practitioners and/or researchers should be aware of the potential biases when using ADP to estimate %BF in older populations
