Screening for childhood obesity: international vs population-specific definitions. Which is more appropriate?

Abstract

AIM:The objectives of this study are: (1) to study the relation between body mass index (BMI), percentage-weight-for-height (PWH) and percentage body fat (PBF) in Singaporean Chinese children; (2) to assess the applicability of an international definition of obesity (the International Obesity Task Force (IOTF) BMI) as a screening tool to detect childhood obesity, as compared with the current Singapore population-specific definition using PWH. METHODS: A total of 623 Chinese children aged 6-11 y (321 males, 302 females) were recruited from a school by proportionate (40%) stratified random sampling. BMI and PWH were calculated from weight and height, while PBF was derived using leg-to-leg bioelectrical impedance analysis. The strength of association among the three indices of obesity was assessed using Spearman's correlation coefficient. Obese children were defined as those above the 95th percentile of PBF in each agegender-specific group. Sensitivity and specificity of IOTF-BMI cutoff values and PWH cutoff values were compared by testing their ability to correctly identify obese children. RESULTS: All three indices correlated well with one another (BMI:PWH r ¼ 0.83, BMI:PBF r ¼ 0.87, PWH:PBF r ¼ 0.76). Prevalence of obesity was lower using IOTF-BMI cutoffs (6.9%) than using PWH cutoffs (16.4%). The sensitivity and specificity of IOTF-BMI cutoff values were 75.0 and 96.0%, respectively, with sensitivity differing between boys (83.3%) and girls (66.6%) (P ¼ 0.35). In comparison, PWH cutoff values had higher sensitivity (91.6%) but lower specificity (86.6%), with no significant difference between the genders. CONCLUSION: IOTF-recommended BMI cutoff values had low sensitivity and may underestimate the local prevalence of childhood obesity. For screening purposes, we recommend that population-specific measures rather than international cutoff values be used.

Evaluation of BMI-based classification of adolescent overweight and obesity: choice of percentage body fat cutoffs exerts a large influence. The COMPASS study

“…The highly specific but less sensitive nature of BMI-based classification systems has been documented repeatedly, despite variations in cutoffs used (Sardinha et al, 1999;Reilly et al, 2000;Fu et al, 2003;Neovius et al, 2004;Zimmermann et al, 2004). The estimates of sensitivity and specificity have, however, varied greatly in these previous studies.…”

“…Several previous studies have defined paediatric obesity and overweight as the fattest 5 and 15%, respectively, in the sample (Lazarus et al, 1996;Reilly et al, 2000;Fu et al, 2003). This method sets the %BF-based prevalence to a fixed percentage, and even though individuals with higher %BF relative to the group may be identified, the cutoffs may vary between studies.…”

Diagnostic accuracy of the BMI for age in paediatrics

“…11 Diagnostic accuracy of national and 'international' obesity definitions Diagnostic accuracy of BMI for age depends on whether it is defined relative to national BMI reference data, or to the 'international' or 'IOTF' definitions of paediatric overweight and obesity. 12 Four published studies [13][14][15][16] have now made a direct comparison of the diagnostic ability of cutoffs based on national reference data (from the US, UK, and Singapore) with those recommended by the IOTF. All four found that the sensitivity of the IOTF obesity definition was much lower than that of definitions based on national reference data (such as BMI X95th percentile).…”

“…Up to 40-50% of the fattest children were not identified as obese by the IOTF approach. [13][14][15][16] These studies also reported that the sensitivity of the IOTF definition was highly sex-specific. In the UK, for example, use of the IOTF approach has much lower sensitivity in boys than girls, 13 leading to the erroneous conclusion that obesity is more prevalent in girls than boys.…”

“…The research on this question in children and adolescents is less advanced, but it seems likely that such population differences are not confined to adulthood. 11,14,20 Ultimately, population-specific BMI cutoffs may therefore become necessary for children and adolescents. 11,14,20 Barriers to use of the BMI for age…”