Study on different sites of waist circumference and its relationship to weight-for-height index in Thai adolescents.

Objective: To compare waist circumference (WC) measured at different sites of trunk region and to determine predictive WC values that were corresponding to weight-for-height index in Thai adolescents.

Material And Method: The authors conducted the cross-sectional study in 509 adolescents, aged 10-18 years old WC was measured at four different sites of trunk region, WC1; at midway between the lowest rib and the iliac crest, WC2; at the narrowest waist, WC3; at immediately above the iliac crest and WC4; at the umbilicus level. Receiver operating characteristic analysis was also performed to determine WC cutoffs to maximize the sensitivity and specificity.

Results: WC measured at all four sites provided small different powerful value in prediction of trunk fat and total body fat (TBF) in adolescents and that WC4 provided slightly better predictive value than other WC. In boys, WC provided better prediction of trunk fat than the prediction of TBF, whereas in girls, the prediction of trunk fat and TBF from WC were of similar magnitude. By receiver operating characteristic analysis, WC risk threshold for predicting the overweight adolescents using Thai weight-for-height Z score > or = 1.5 SD as reference was 73.5 cm for boys (sensitivity 96.8%, specificity 85.7%) and 72.3 cm for girls (sensitivity 96.1%, sensitivity 80.5%). WC threshold was increased to 75.8 cm. (sensitivity 96.3.%, specificity 86.4%) for boys and 74.6 cm for girls (sensitivity 95.1%, specificity 85.7%) in order to detect the obese children.

Conclusion: Waist circumference has been proposed as the simple tool for screening the overweight adolescents and when measured at the umbilicus level, it is considered the feasible site for self-evaluation. Further study is needed to investigate the relationship between the increased WC and metabolic risk factors for obesity in adolescents.