Measuring severe obesity in pediatrics using body mass index-derived metrics from the Centers for Disease Control and Prevention and World Health Organization: a secondary analysis of CANadian Pediatric Weight management Registry (CANPWR) data.

To examine the (i) relationships between various body mass index (BMI)-derived metrics for measuring severe obesity (SO) over time based the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) references and (ii) ability of these metrics to discriminate children and adolescents based on the presence of cardiometabolic risk factors. In this cohort study completed from 2013 to 2021, we examined data from 3- to 18-year-olds enrolled in the CANadian Pediatric Weight management Registry. Anthropometric data were used to create nine BMI-derived metrics based on the CDC and WHO references. Cardiometabolic risk factors were examined, including dysglycemia, dyslipidemia, and elevated blood pressure. Analyses included Pearson correlations, intraclass correlation coefficients (ICC), and receiver operator characteristic area-under-the-curve (ROC AUC). Our sample included 1,288 participants (n = 666 [52%] girls; n = 874 [68%] white). The prevalence of SO varied from 60-67%, depending on the definition. Most BMI-derived metrics were positively and significantly related to one another (r = 0.45-1.00); ICCs revealed high tracking (0.90-0.94). ROC AUC analyses showed CDC and WHO metrics had a modest ability to discriminate the presence of cardiometabolic risk factors, which improved slightly with increasing numbers of risk factors. Overall, most BMI-derived metrics rated poorly in identifying presence of cardiometabolic risk factors.    Conclusion: CDC BMI percent of the 95 percentile and WHO BMIz performed similarly as measures of SO, although neither showed particularly impressive discrimination. They appear to be interchangeable in clinical care and research in pediatrics, but there is a need for a universal standard. WHO BMIz may be useful for clinicians and researchers from countries that recommend using the WHO growth reference. What is Known: • Severe obesity in pediatrics is a global health issue. • Few reports have evaluated body mass index (BMI)-derived metrics based on the World Health Organization growth reference. What is New: • Our analyses showed that the Centers for Disease Control and Prevention BMI percent of the 95 percentile and World Health Organization (WHO) BMI z-score (BMIz) performed similarly as measures of severe obesity in pediatrics. • WHO BMIz should be a useful metric to measure severe obesity for clinicians and researchers from countries that recommend using the WHO growth reference.