Body mass index and childhood obesity classification systems: A comparison of the French, International Obesity Task Force (IOTF) and World Health Organization (WHO) references.

AIM: This study aims to compare three body mass index (BMI)-based classification systems of childhood obesity: the French, the International Obesity Task Force (IOTF) and the World Health Organization (WHO) references. METHODS: The study involved 1382 schoolchildren, recruited from the Lille Academic District in France in May 2009 aged 8.4+/-1.7 years (4.0-12.0 years). Their mean height and body mass were 131.5+/-10.9cm and 30.7+/-9.2kg, respectively, resulting in a BMI of 17.4+/-3.2kg/m(2). The weight status was defined according to the three systems considered in this study. The agreement between these references was tested using the Cohen's kappa coefficient. RESULTS: The prevalence of overweight was higher with the WHO references (20.0%) in comparison with the French references (13.8%; P<0.0001) and the IOTF (16.2%; P</=0.01). A similar result was found with obesity (WHO: 11.6% vs. IOTF: 6.7%; or French references: 6.7%; P<0.0001). Agreement between the three references ranged from "moderate" to "perfect" (0.43</=kappa</=1.00; P<0.0001). Kappa coefficients were higher when the three references were used to classify children as obese (0.63</=kappa</=1.00; P<0.0001) as compared to classification in the overweight (obesity excluded) category (0.43</=kappa</=0.94; P<0.0001). When sex and age categories (4-6 years vs. 7-12 years) were considered to define the overweight status, the lowest kappa coefficient was found between the French and WHO references in boys aged 7-12 years (kappa=0.28; P<0.0001), and the highest one in girls aged 7-12 years between the French references and IOTF (kappa=0.97; P<0.0001). As for obesity, agreement between the three references ranged from 0.60 to 1.00 (P<0.0001), with the lowest values obtained in the comparison of the WHO references against French references or IOTF among boys aged 7-12 years (kappa=0.60; P<0.0001). CONCLUSION: Overall, the WHO references yield an overestimation in overweight and/or obesity within this sample of schoolchildren as compared to the French references and the IOTF. The magnitude of agreement coefficients between the three references depends on of both sex and age categories. The French references seem to be in rather close agreement with the IOTF in defining overweight, especially in 7-12-year-old children.