The identification of children with adverse risk factor levels by body mass index cutoffs from 2 classification systems the Bogalusa Heart Study

Background The cutoffs from the Centers for Disease Control and Prevention (CDC) growth charts and from the Cooper Institute (Fitness Gram) are widely used to identify children who have a high body mass index (BMI) Objective We compared the abilities of these 2 systems to identify children who have adverse lipid concentrations and blood pressure measurements and the reliability (consistency) of each classification system over time (mean follow up 7 y) Design A cross sectional analysis based on data from 22 896 examinations of 5 to 17 y olds was conducted Principal components analyses were used to summarize levels of the 5 risk factors and likelihood ratios and the h statistic were used to compare the screening abilities of the 2 systems Of these children 3972 were included in longitudinal analyses Results There were marked differences in the prevalence of a high Fitness Grain BMI by age with the prevalence among boys increasing from 2 5% to 21% between the ages of 5 and 11 y The identification of adverse risk factors by the 2 systems was only fair kappa = 0 25) but there was little difference in the abilities of the CDC and Fitness Gram cutoffs to identify high risk children Longitudinal analyses however indicated that the agreement between initial and follow up Fitness Gram classifications was substantially lower than that based on CDC cutoffs (K = 0 28 compared with 0 49) Conclusions The Fitness Gram and CDC cutoffs have similar abilities to identify high risk children However a high Fitness Gram BMI is difficult to interpret because the reliability over time is low and the prevalence increases markedly with age Am J Clm Nutr 2010 92 1298-305