[Determination of the most relevant body mass index standard references to define obese Iranian school-age children]

ABSTRACT

To define overweight and obesity in children, body mass index [BMI] reference standards are used. Presently four reference standards can be used to determine obesity among children in Iran CDC-2000 standard, IOTF-2000 standard, the recent [2007] WHO growth references for school-age children and adolescents, and finally, the Iranian reference cutoffs, developed in 1999. So far there has been no study in Iran on identifying the best BMI reference standard for Iranian obese children. This study was conducted to identify the most suitable BMI reference standard to define obesity among Iranian children, as compared with triceps skin fold thickness. A total of 6818 school-age children [6-11years old] were recruited from 3 Iranian cities, namely, Ahwaz, Kazeroon, Orumiyeh, and Yazd by random cluster sampling. Age, sex, weight]to the nearest 0.1 kg], height [to the nearest 0.1 cm] and triceps skinfold thickness [TSF, to the nearest 0.1 mm] were determined and BMI was calculated. Obesity was defined as a BMI >/= 95th percentile of CDC, WHO, and the Iranian reference standard. With regard to the IOTF standard, cutoff points [for boys and girls] were chosen as percentiles that matched the adult cutoffs of BMI of 30 at 18 years of age. The 95th percentile of TSF for each age/sex group was determined in each city and 5% of the pupils with the highest TSF [true obese children] were selected. Analysis was done on data gathered on 6700 subjects.Based on TSF, approximately 5% of the children were identified as obese. Proportions of obese children according to CDC, IOTF, WHO, and the Iranian reference standard were 5.4%, 3.9%, 6.3%, and 13.6%, respectively. Kappa values showed moderate agreement between the 4 reference values and TSF among the children [0.44-0.60]. Overall, the Iranian reference standard showed the lowest agreement [0.44]. Sensitivities and specificities of the 4 reference standards were, respectively, 61% and 97.5% for CDC, 98.8% and 55% for IOTF, 97% and 69.2% for WHO, and 90.4% and 90.3% for the Iranian reference values. The Iranian reference proved to have the lowest positive predictive value [PPV+] and efficiency.Despite the high sensitivity of the Iranian reference standard, its PPV+ [prevalence rate of disease], the most important diagnostic character of a method, and its efficiency were low in comparison with the other standards. Based on the findings of this study and features of the recent WHO growth reference values, we recommend the use of the WHO reference in future studies to assess obesity in children