Comparison of waist circumference percentiles versus body mass index percentiles for diagnosis of obesity in a large cohort of children

CONTEXT: Waist circumference may offer improved diagnosis of obesity in youth compared with body mass index (BMI), but empirical evidence is limited. OBJECTIVE: To compare the ability of BMI percentile using UK reference data and waist circumference percentile using UK reference data to diagnose high fat mass in English children. DESIGN AND METHODS: In 7,722 9-10-year-olds (3,809 boys, 3,913 girls) sensitivity and specificity were calculated and receiver operator characteristic (ROC) analyses undertaken to determine the diagnostic accuracy of BMI and waist circumference z-scores to define high fat mass measured by dual energy x-ray absorptiometry (DXA). High fat mass was defined as being in the top decile of fatness for each sex (359 boys and 367 girls). RESULTS: The area under the ROC curve was slightly higher for BMI percentile (0.92 in boys, 95% CI: 0.91 -0.93; 0.94 in girls, 95% CI: 0.93-0.95) than waist circumference percentile (0.89 in boys, 95% CI: 0.86-0.91; 0.81 in girls, 95% CI: 0.73-0.90). Specificity of BMI percentile was slightly but significantly higher than that of waist circumference percentile for both sexes (p<0.05 in each case). CONCLUSIONS: The present study suggests that waist circumference percentile has no advantage over BMI percentile for the diagnosis of high fat mass in children.