Use of Air Displacement Plethysmography in the Determination of Percentage of Fat Mass in African American Children

The purpose of this study was to determine the ability of air displacement plethysmography (ADP) to estimate percentage of fat mass (%FM) in African American children. %FM was determined in 21 boys and 13 girls (11.0 ± 1.4 y, 18.6 ± 4.2 kg/m2 [mean ± SD]) by ADP (using six published densitometric equations) and dual-energy x-ray absorptiometry (DXA). Measures were done within 2 h of one another, in random order. Regardless of equation, %FMADP was significantly correlated with %FMDXA (R2 = 0.67–0.71, all p < 0.001). %FMADP using the equation of Siri (%FMADP-Siri 20.3 ± 9.0) agreed most closely with %FMDXA (20.0 ± 10.2, difference p = 0.729). Together, surface area artifact and bone mineral content per unit of bonefree fat-free mass accounted for 29% of the variance in the residual between methods. The correlation between %FMADP-Siri and %FMDXA was not significant for those <35 kg (n = 10; R2 = 0.084, p = 0.417). There was a trend toward %FMADP-Siri underestimating %FMDXA in girls (−1.46 ± 3.0%FM; p = 0.103) but not in boys (1.43 ± 6.4%FM; p = 0.315). Predicted lung volume was 40.1% higher than measured lung volume (p < 0.001). %FMADP-Siri determined using predicted lung volume was 23.5 ± 8.9, higher than that using measured lung volume (p = 0.001) and higher than %FMDXA (p = 0.001). We conclude that in 9- to 14-y-old African American children and provided lung volume is measured, %FM using ADP with Siri's equation approximates that obtained by DXA. Body composition results determined by ADP in children <35 kg should be interpreted with caution.