Severe obesity is a limitation for the use of body mass index standard deviation scores in children and adolescents

Aim We analysed the distribution of the body mass index standard deviation scores (BMI-SDS) in children and adolescents seeking treatment for severe obesity, according to the International Obesity Task Force (IOTF), World Health Organization (WHO) and the national Norwegian Bergen Growth Study (BGS) BMI reference charts and the percentage above the International Obesity Task Force 25 cut-off (IOTF-25). Methods This was a cross-sectional study of 396 children aged four to 17 years, who attended a tertiary care obesity centre in Norway from 2009 to 2015. Their BMI was converted to SDS using the three growth references and expressed as the percentage above IOTF-25. The percentage of body fat was assessed by bioelectrical impedance analysis. Results Regardless of which BMI reference chart was used, the BMI-SDS was significantly different between the age groups, with a wider range of higher values up to 10 years of age and a more narrow range of lower values thereafter. The distributions of the percentage above IOTF-25 and percentage of body fat were more consistent across age groups. Conclusions Our findings suggest that it may be more appropriate to use the percentage above a particular BMI cut-off, such as the percentage above IOTF-25, than the IOTF, WHO and BGS BMI-SDS in paediatric patients with severe obesity.