Comparison of different BMI cut-offs to screen for child and adolescent obesity in urban China

To determine which set of BMI cut-offs is the most appropriate to define child and adolescent obesity in urban China.

A cross-sectional study was carried out between 1 November and 31 December in 2017.

Community Healthcare Center in Minhang District, Shanghai, China.

A total of 12 426 children and adolescents aged 7-17 years were selected by cluster random sampling. Bioelectrical impedance analysis was the gold standard to measure body composition.

Comparisons of three sets of BMI cut-offs by sensitivity and κ value revealed that the Working Group on Obesity in China (WGOC) (sensitivity 39·9-84·0 %; κ 0·51-0·79) and WHO (sensitivity 25·5-74·5 %; κ 0·35-0·78) cut-offs were not superior to the International Obesity Task Force (IOTF) (sensitivity 47·9-92·4 %; κ 0·58-0·85) cut-offs across all subgroups. The WGOC and WHO cut-offs yielded higher misclassification rates, in the worst case, categorising 11·2 % of girls with high adiposity as normal and 44·4 % of them as overweight, while the IOTF cut-offs categorised 2·3 % as normal and 30·7 % as overweight. Individuals who were classified by the IOTF cut-offs as overweight had the lowest ratios of high adiposity (4·2-41·6 %) than by the BMI cut-offs for each subgroup. Among pubertal girls, none of the BMI-based cut-offs indicated excellent agreement with body fat percentage, and κ value of the WHO cut-offs (0·35 (95 % CI 0·29, 0·41)) was lower than the other two sets of BMI cut-offs (all P < 0·001).

The IOTF cut-offs for Asian should be recommended for child obesity screening in urban China. Pubertal individuals need a more accurate indicator of obesity screening.