Estimates of percentage body fat in young adolescents: a comparison of dual-energy X-ray absorptiometry and air displacement plethysmography

Objective: To evaluate the accuracy of percentage body fat (% fat) estimates from air displacement plethysmography ( ADP) against an increasingly recognised criterion method, dual-energy X-ray absorptiometry (DXA), in young adolescents. Design: Cross-sectional evaluation. Setting: Leeds General Infirmary, Centre for Bone and Body Composition Research, Leeds, UK. Subjects: In all, 28 adolescents (12 males and 16 females), age (mean+/-s.d.) 14.9+/-0.5 y, body mass index 21.2+/-2.9 kg/m(2) and body fat (DXA) 24.2+/-10.2% were assessed. Results: ADP estimates of % fat were highly correlated with those of DXA in both male and female subjects (r = 0.84 - 0.95, all P<0.001; s.e.e. = 3.42 - 3.89%). Mean % fat estimated by ADP using the Siri (1961) equation (ADP(Siri)) produced a nonsignificant overestimation in males (0.67%), and a nonsignificant underestimation in females (1.26%). Mean % fat estimated by ADP using the Lohman (1986) equations (ADP(Loh)) produced a nonsignificant underestimation in males (0.90%) and a significant underestimation in females (3.29%; P<0.01). Agreement between ADP and DXA methods was examined using the total error (TE) and methods of Bland and Altman (1986). Males produced a smaller TE (ADP(Siri) 3.28%; ADP(Loh) 3.49%) than females (ADP(Siri) 3.81%; ADP(Loh) 4.98%). The 95% limits of agreement were relatively similar for all % fat estimates, ranging from +/-6.57 to +/-7.58%. Residual plot analyses, of the individual differences between ADP and DXA, revealed a significant bias associated with increased % fat ( DXA), only in girls (P<0.01). Conclusions: We conclude that ADP, at present, has unacceptably high limits of agreement compared to a criterion DXA measure. The ease of use, suitability for various populations and cost of ADP warrant further investigation of this method to establish biological variables that may influence the validity of body fat estimates.