Classification of childhood obesity using longitudinal clinical body mass index and its validation.

: Persistence of childhood adiposity is known to be associated with long-term adverse cardiometabolic risks. Yet, cross-sectional body mass index (BMI) is often used to classify obesity in clinical care and research. This study aimed to develop and validate a childhood obesity classification system using longitudinal clinical data. : This observational study used electronic health record data from a tertiary care hospital, with replication in an independent cohort. For individuals with ≥ 3 BMI measurements, the median BMI percentile and persistence in the obesity class were used for longitudinal classification. The association between longitudinal BMI class and early onset obesity, socioeconomic status (SES), and adverse cardiometabolic risk was analyzed. : Height, weight, and cardiometabolic risk measures were obtained for 22 352 children from 2014-18 in the primary cohort and 24 444 children in the replication cohort. Obesity (BMI ≥ 95 percentile [BMI ]) was observed in 24.1% and severe obesity (BMI ≥ 120% of BMI ) in 10.6%. Individuals with early onset obesity (age ≤ 6 years) remained in the same or higher obesity class; those in the high-SES group had lower odds of obesity. The proportion of individuals with cardiometabolic risk increased with increasing obesity severity (p-value 0.01 - < 0.001). The AUC for cardiometabolic risk by longitudinal BMI class was higher compared to that for cross-sectional BMI (80.0% vs. 75.8%, p < 0.001). The Longitudinal BMI classification may better reflect long-term cardiometabolic risk in children. This classification can be useful for focused intervention strategies and for profiling of individuals for genetic testing.