[Body mass index cut-offs for overweight and obesity in Chinese children and adolescents aged 2 - 18 years].

Objective: To study the body cut-offs of mass index (BMI) for the purpose of screening overweight and obesity for Chinese children and adolescents aged 2 - 18 years.

Methods: Based on the BMI growth reference values for Chinese children aged 0 - 18, using the common methods to establish the BMI cut-offs for screening overweight and obesity. These methods were having the same empirical percentile or Z scores and the BMI value at 18 years consistent with adults. Three sets of BMI cut-offs, including (BMI₂₄, BMI₂₈), (P₈₅, P₉₅) and (Z₁, Z₂), were initially identified. Differences were compared on different cut-off points and prevalence rates of overweight and obesity with different BMI reference, different values and "prevalence" of overweight and obesity based on "2004 Beijing Child and Adolescent Metabolic Syndrome Study". Cut-offs standards which recommended by the Chinese Working Group on Obesity for Children (WGOC) and by the International Obesity Task Force (IOTF) were also used. Finally the appropriate cut-offs were defined.

Results: Three sets of BMI cut-offs for screening overweight and obesity for Chinese children and adolescents aged 2 - 18 years were obtained according to the above mentioned methods for selection. The prevalence rates of overweight and obesity defined by those cut-offs appeared not to be significantly different. Compared with the WGOC, the BMI cut-off points for screening overweight and obesity for both boys and girls from our study were very close to the WGOC', but cut-off points for screening overweight for girls aged 8.5 - 15.5 y was 0.3 - 1.0 kg/m² lower than the WGOC'. Going through the database on screening of "2004 Beijing Children's Metabolic Syndrome Survey", the prevalence of overweight for girls was about 3.4% higher than using the cut-offs of WGOC.

Conclusion: Results from this study suggested that the BMI cut-offs passed through the cut-off point of BMI₂₄ and BMI₂₈ at 18 years was appropriate for screening overweight and obesity in Chinese children from 2 to 18 years, and achieved the continuity in age and consistency in screening standard when using the BMI indicator in children and adolescents.