Is air-displacement plethysmography a reliable method of detecting ongoing changes in percent body fat within obese children involved in a weight management program?

Summary Background The prevalence of childhood obesity in the US has increased considerably over the last few decades and continues to increase. To monitor the progress of patients enrolled in weight management programs, clinicians need accurate methods of detecting changes in body composition (percent body fat) over time. The gold standard method, hydrodensitometry, has severe limitations for the pediatric population. Objective This study examines the reliability of air-displacement plethysmography (ADP) in detecting percent body fat changes within obese children over time. Methods Percent body fat by ADP, weight, and body mass index (BMI) were measured for eight obese children aged 5–12 years enrolled in a weight management program over a 12-month period. These measurements were taken at initial evaluation, 1.5 months, 3 months, 6 months, and 12 months to monitor the progress of the subjects and detect any changes in these measures over time. Statistical analysis was used to determine the reliability of the data collected. Results The reliability estimate for percent body fat by ADP was 0.78. This was much lower than the reliability of BMI, 0.98, and weight measurements, 0.99. The low reliability estimate of ADP indicates a large standard error of measurement by this method. Conclusion The measurement error of ADP is large, and in our study, ADP measured changes in percent body fat that far exceeded levels of true change that would have been clinically useful and important to detect. Hence, this method yielded change measures that did not allow meaningful clinical interpretations and often did not reflect true differences in status across time. ADP is not a reliable method for detecting changes in percent body fat over the time intervals employed within this study of obese children.