Diagnostic accuracy of different body weight and height-based definitions of childhood obesity in identifying overfat among Chinese children and adolescents: a cross-sectional study

BACKGROUND: Various body weight and height-based references are used to define obese children and adolescents. However, no study investigating the diagnostic accuracies of the definitions of obesity and overweight in Hong Kong Chinese children and adolescents has been conducted. The current study aims to investigate the diagnostic accuracy of BMI-based definitions and 1993 HK reference in screening excess body fat among Hong Kong Chinese children and adolescents. METHODS: A total of 2,134 participants (1,135 boys and 999 girls) were recruited from local schools. The foot-to-foot BIA scale was applied to assess %BF using standard methods. The criterion of childhood obesity (i.e., overfat) was defined as over 25 %BF for boys and over 30 %BF for girls. Childhood obesity was also determined from four BMI-based references and the 1993 HK reference. The diagnostic accuracy of these existing definitions for childhood obesity in screening excess body fat was evaluated using diagnostic indices. RESULTS: Overall, %BF was significantly correlated with anthropometry measurements in both genders (in boys, r = 0.747 for BMI 0.766 for PWH; in girls, r = 0.930 for BMI 0.851 for PWH). The prevalence rates of overweight and obesity determined by BMI-based references were similar with the prevalence rates of obesity in the 1993 HK reference in both genders. All definitions for childhood obesity showed low sensitivity (in boys, 0.325–0.761; in girls, 0.128–0.588) in detecting overfat. Specificities were high for cut-offs among all definitions for childhood obesity (in boys, 0.862–0.980; in girls, 0.973–0.998). CONCLUSIONS: In conclusion, prevalence rates of childhood obesity or overweight varied widely according to the diagnostic references applied. The diagnostic performance for weight and height-based references for obesity is poorer than expected for both genders among Hong Kong Chinese children and adolescents. In order to improve the diagnosis accuracy of childhood obesity, either cut-off values of body weight and height-based definitions of childhood obesity should be revised to increase the sensitivity or the possibility of using other indirect methods of estimating the %BF should be explored.