Objective: To evaluate the prevalence, sensitivity and specificity of two risk classifications of obesity based on the body mass index (BMI).
Methods: Five-hundred and two adolescents, aged 12-18 years, participants of a health and nutrition survey conducted in 1996 in the city of Rio de Janeiro, Brazil, were evaluated. The study variables included: weight, stature, BMI, and subscapular skinfold, according to sex and age. The BMI classifications were compared to a fatness classification based on the 90th percentile of subscapular skinfold thickness in American adolescents.
Results: The prevalence of risk of obesity was higher when using the subscapular skinfold measurement (p<0.0001), compared to both BMI-based classifications, which showed similar values. Specificity was higher than sensitivity in both BMI-based classifications. The balance between sensitivity and specificity was close to the 70thBMI percentile for boys and girls below 14 years old. For boys older than 15 the cutoff value was the 50th percentile.
Conclusion: Both BMI-based classifications were more suitable to identify adolescents without obesity, and their sensitivities were too low for tracking risk of obesity.