Background: BMI measures are often used to infer body composition. Bioelectrical impedance analysis (BIA) is a more accurate way to estimate percent body fat (%BF), particularly when screening children who may be overweight. The aim of this study was to determine the validity, sensitivity to change, and diagnostic value of a BIA scale designed specifically for adolescents.
Methods: One hundred twelve adolescents had their body fat assessed using both BIA and dual-energy X-ray absorptiometry (DEXA). Mean difference and limits of agreement (LoA) were calculated for criterion validity. Intraclass correlation coefficients (ICCs) were calculated for sensitivity to change. Sensitivity/specificity for each classification was also assessed. Data from 46 returning adolescents (6-8 months later) were then used to assess sensitivity to change of BIA compared with DEXA.
Results: ICC for absolute agreement (range) comparing BIA and DEXA was 0.78 (0.48-0.88). The mean difference between the BIA %BF reading and DEXA was -4.05% (LoA = [4.80%, -12.90%]). Sensitivity and specificity values for the underfat, healthy, overfat, and obese classifications were 0.0/0.89, 0.79/0.46, 0.28/0.92, and 0.5/1.00, respectively. ICC for absolute agreement over time between the BIA %BF and the DEXA %BF was 0.71 (0.242-0.866).
Conclusions: The Tanita BF-689 demonstrated poor-good agreement with DEXA when measuring %BF, poor-moderate agreement when measuring change in %BF over time, high sensitivity for classification into the healthy category and high specificity for classification into the underfat/overfat/obese categories. Compared to DEXA, the BF-689 is accurate, accessible, and efficient in classifying adolescents based on %BF.
Keywords: DEXA; adolescent obesity; bioelectrical impedance; percent body fat.