Receiver operating characteristic analysis of body mass index, triceps skinfold thickness, and arm girth for obesity screening in children and adolescents.

BACKGROUND: Valid and practical methods based on health-related criteria for obesity screening in children and adolescents are not available. Arbitrarily defined body mass index (BMI) cutoffs have been proposed to select adolescents at high risk of developing obesity in adulthood.
OBJECTIVE: We assessed the usefulness of BMI, triceps skinfold thickness, and upper arm girth for screening for obesity by using a health-related definition of obesity (> or = 25% body fat in boys and > or = 30% body fat in girls) and a criterion method (dual-energy X-ray absorptiometry) that estimates percentage fat without the potential bias associated with other methods in adolescents.
DESIGN: This was a cross-sectional study of Portuguese boys (n = 165) and girls (n = 163) aged 10-15 y. Nonparametric receiver operating characteristic (ROC) analysis was used to define the best tradeoff between true-positive and false-positive rates.
RESULTS: True-positive rates ranged from 67% to 87% and from 50% to 100% in girls and boys, respectively, and false-positive rates ranged from 0% to 19% and from 5% to 26%, respectively. For children aged 10-11 y, the areas under the curves (AUCs) for ROCs, an index of diagnostic accuracy, were close to 1.0, suggesting very good accuracy. For older boys and girls, AUCs for triceps skinfold thickness were similar to or greater than AUCs for BMI and upper arm girth.
CONCLUSIONS: The results suggest that triceps skinfold thickness gives the best results for obesity screening in adolescents aged 10-15 y. BMI and upper arm girth were reasonable alternatives, except in 14-15-y-old boys, in whom both indexes were only marginally able to discriminate obesity.