Cut-off Values of Body Mass Index, Waist Circumference, and Waist-to-Height Ratio to Identify Excess Abdominal Fat: Population-Based Screening of Japanese Schoolchildren

Background: School-based screening and prevention programs for adiposity generally target school children in grades 4 and 6 (age 9-11 years). The aims of this study were to evaluate the validity of body mass index (BMI), waist circumference (WC), and waist-to-height ratio (WHtR) in identifying abdominal adiposity in fifth-grade Japanese school children and to determine optimal cut-off values for anthropometric measures. Methods: The target population was fifth-grade school children enrolled in 2 schools in Shizuoka, Japan between 2008 and 2010; 422 of the 466 children participated in the present study. Abdominal adiposity was defined as percent trunk fat in the 95th percentile or higher, as determined by dual-energy x-ray absorptiometry (DXA). We analyzed the validity of BMI, WC, and WHtR using receiver operating characteristic (ROC) curve analysis. The Youden index was used to determine cut-off values of BMI, WC, and WHtR that identify excess abdominal fat. Results: Optimal cut-off values to identify abdominal adiposity were 20.8 kg/m(2) (BMI), 76.5 cm (WC), and 0.519 (WHtR) for boys, and 19.6 kg/m(2) (BMI), 73.0 cm (WC), and 0.499 (WHtR) for girls. Areas under the ROC curve were 0.983 (BMI), 0.987 (WC), and 0.981 (WHtR) for boys, and 0.981 (BMI), 0986 (WC), and 0.992 (WHtR) for girls. Conclusions: BMI, WC, and WHtR successfully identified a high proportion of children with excess abdominal fat as measured by DXA, demonstrating that these measures are useful indices for school screening.