Screening performances of the International Obesity Task Force body mass index cut-off values in adolescents.

OBJECTIVE: To try to improve the International Obesity Task Force (IOTF) BMI cut-off values, in terms of prediction of body fat percentage assessed by dual-energy X-ray absorptiometry (DXA), in adolescents.

METHODS: Cross-sectional survey of the adolescents from the city of Zaragoza (Spain). For this analysis we have included 286 adolescents (116 boys and 170 girls) aged 13.0-17.9 years. Body mass index (BMI) was calculated as body weight (kg), divided by height (m) squared. The percentage of body fat (BF%) was estimated by the use of DXA.

RESULTS: We have calculated, new BMI cut-off values (AVENA cut-offs) to predict BF%, for boys and girls in each age group. In male adolescents, sensitivity was higher with the IOTF cut-offs (0.71, 95th C.I.: 0.44, 0.90) than with the AVENA ones (0.53, 95th C.I.: 0.28, 0.77), and specificity was very similar with both cut-off values (0.86 and 0.88, respectively), the differences being not statistically significant. In girls, both sensitivities (0.75 and 0.79, respectively) and specificities (0.90 and 0.92, respectively) were very similar with both cut-off values, and the differences, not significant.

CONCLUSIONS: Optimization of the IOTF BMI cut-off values, in terms of BF%, seems not to be possible in adolescents. The IOTF criteria should be used only for overweight and obesity screening; however, in clinical settings, a more accurate measure of body fat should be recommended.