Title of article:

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

Authors: Sardinha LB, Going SB, Teixeira PJ, Lohman TG.
Journal: Am J Clin Nutr, Dec 1999 ;70(6):1090-5

Abstract

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.

Comments and Key points

This article recommends optimum Body Mass Index threshold values to define obesity:

BMI threshold	Boys	Girls
Age 10-11	19.0	19.6
Age 12-13	19.4	21.2
Age 14-15	24.0	21.9

It's a good article from a perfectly conducted study. The population sample came from Lisbon, Portugal, which is the only factor that makes the results seem potentially not applicable to other nationalities.

But as these charts show, their recommendations, (labeled as blue dots "Lisbon Obesity") are quite a bit lower than the CDC's definition of obesity at the 95^th percentile line of BMI for age.

But, compared to the CDC's definition of overweight at the 85^th percentile line of BMI for age, the Lisbon thresholds seem more appropriate.

A closer reading of this article, shows they actually were thinking about the 85^th percentile, but they seem to be unwilling to use the word "overweight". I guess that's the only confusing thing about this study. Obviously, their results should be interpreted as an "overweight" threshold for adolescents, which corresponds to >=25% body fat for boys and >= 30% body fat for girls.

Review & comments by Steven B. Halls, MD, Last edited 23 June, 2008, Copyright
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