BMI and Waist Circumference in Predicting Cardiovascular Risk Factor Clustering in Chinese Adolescents

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Abstract
To derive the optimal BMI and waist circumference (WC) cut-off values to predict clustering of cardiovascular risk factors in Hong Kong Chinese adolescents. A total of 2102 Hong Kong Chinese 12 to 19 years of age were recruited. Participants were considered to have clustering of risk factors if at least three of the following risk factors were present: 1) high-density lipoprotein cholesterol (HDL-C) < or = 1.03 mM, 2) low-density lipoprotein cholesterol (LDL-C) > or = 2.6 mM, 3) triglyceride (TG) > or = 1.24 mM, 4) fasting plasma glucose (FPG) >/=6.1 mM, and 5) age-, sex-, and height-adjusted systolic or diastolic blood pressure (BP) > or = 90th percentile. Receiver operating characteristics (ROC) curves were generated to identify the optimal age-adjusted BMI and WC cut-off values to predict clustering of risk factors in boys and girls separately. These age-adjusted BMI and WC cut-offs were transformed to percentile values. Cole's lambda-mu-sigma (LMS) method was used to obtain smoothed age-specific BMI and WC at these percentile values. The areas under ROC curves for BMI in girls and boys were 0.85 [95% confidence interval (CI), 0.77 to 0.92] and 0.76 (95% CI, 0.66 to 0.85), respectively. The respective areas under ROC curves for WC in girls and boys were 0.82 (95% CI, 0.74 to 0.91) and 0.78 (95% CI, 0.68 to 0.87). The optimal BMI thresholds were at the 78th percentile for girls and the 72nd percentile for boys. The respective values for WC were at the 77th percentile for girls and the 76th percentile for boys. The sensitivities and specificities of these cut-off values ranged from 72% to 80%. Age- and sex-specific BMI and WC cut-off values can be used to identify adolescents with clustering of cardiovascular risk factors.