Body composition in children and adults by air displacement plethysmography

Objectives: Air displacement plethysmography (ADP) may provide a partial al ternative to body density (B-d) and therefore body composition measurement compared to conventional hydrodensitometry (H-d) in children. As there are no evaluation studies of ADP in children, this study had a two-fold objecti ve: to compare E-d estimates by ADP and H-d; and to compare fat estimates b y both ADP and H-d to fat estimates by another reference method, dual energ y X-ray absorptiometry (DXA). Setting: Obesity Research Center, St. Luke's/Roosevelt Hospital, New York, USA. Subjects: One hundred and twenty subjects (66 females/54 males) who ranged in age from 6-86 y and in body mass index (BMI, kg/m(2)) from 14.1-40.0 kg/ m(2) met study entry criteria. Study Design: Cross-sectional study of healthy children (age less than or e qual to 19 y) and adult group for comparison to earlier studies. Each subje ct completed ADP, H-d, and DXA studies on the same day. Only subjects with subjectively-judged successful H-d studies were entered into the study coho rt. Results: There was a high correlation between B-d by ADP and H-d (Bd H-d = 0.11 + 0.896 x B-d ADP; r = 0.93, SEE = 0.008 g/cm(3), P < 0.0001), althoug h the regression line slope and intercept differed significantly from 1 and 0, respectively. Additional analyses localized a small-magnitude B-d bias in the child (n = 48) subgroup. Both ADP and H-d %fat estimates were highly correlated (r > 0.9, P < 0.0001) with %fat by DXA in child and adult subgr oups. Bland-Altman analyses revealed no significant%fat bias by either ADP or H-d vs DXA in either children or adults, although a bias trend (P=0.11) was detected in the child subgroup. Conclusion: With additional refinements, the air displacement plethysmograp hy system has the potential of providing an accurate and practical method o f quantifying body fat in children as it now does in adults.