Body mass index in screening for adiposity in children and adolescents: Systematic evaluation using receiver operating characteristic curves

Body mass index (BMI) has been recommended for use in adolescent screening programs to select subjects with excess body fat for appropriate interventions. No systematic evaluation of BMI in screening for high degrees of adiposity was available when these recommendations were formulated. The purpose of this paper was to evaluate the screening performance of BMI using appropriate epidemiologic methods. Percentage body fat (TBF%) was measured by dual-energy X-ray absorptiometry (DXA) in a convenience sample of 230 (119 males, 111 females) healthy Australian volunteers aged 4-20 y inclusive. Receiver operating characteristic (ROC) curves were prepared for detecting TBF% at or beyond the 85th percentile, using BMI as the screening test. Screening performance was slightly better for girls than for boys, but the differences were not significant. Reasonable true-positive (0.71, 95% CI: 0.53, 0.85) and low false-positive (0.05, 95% CI: 0.02, 0.09) rates were observed at the 85th percentile cutpoint for BMI. At the 95th percentile cutpoint for BMI, both true-positive (0.29, 95% CI: 0.15, 0.47) and false-positive (0.01, 95% CI: 0.00, 0.03) rates were lower. Screening for excess adiposity by using an appropriate percentile cutoff for BMI gives acceptable performance. ROC curves facilitate design of screening programs by allowing an explicit tradeoff between true-positive and false-positive rates. Although large sample sizes are required for precise estimates, the cutoff points that have been recommended appear to offer a reasonable compromise between true- and false-positive rates.