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

Abstract

Objective: To determine the impact of commonly used body fat percentage (%BF) references when evaluating the sensitivity, specificity and misclassifications of body mass index (BMI) for obesity screening in adolescence. Subjects/Methods: A community-based sample of 3334 adolescents aged 15.270.6 years was studied. Weight, height and %BF were measured. Sensitivity, specificity, predictive values and type and extent of misclassifications were calculated. Truepositive subjects for overweight and obesity were defined by recently published paediatric %BF cutoffs, 85th and 95th percentiles from the present study population, and an older %BF reference. Results: Regardless of %BF reference used, specificities were high (40.98 for obesity and 40.90 for overweight) in both sexes, with values for overweight consistently higher for girls (Po0.05). Sensitivities were much lower, with boys ranging from 0.52 to 0.74 for overweight, and 0.24 to 0.43 for obesity. Corresponding sensitivities for girls were 0.42-0.66 and 0.22-0.46. Large discrepancies were seen in total number of misclassifications, with published references resulting in twice as many misclassified for overweight (620, 514 vs 362) when compared to the cutoffs from the study population. For obesity, the difference was even greater (367 vs 133). Conclusions: No matter which %BF reference used, specificity of BMI was high, and sensitivity low for both sexes. Population percentiles resulted in somewhat lower specificity but much higher sensitivity, and many more correctly classified compared to when cutoffs from the literature were used. The choice of %BF reference in evaluations of BMI-based classification systems has a large impact on the outcome. Sensitivity analyses are therefore warranted.

The combined effects of overweight and smoking in late adolescence on subsequent disability pension: a nationwide cohort study

“…14,15 Two other studies on young Swedish males found a small but significantly increased risk for underweight also 16,17 (HR 1.14 in both studies), although only a trend in that direction could be detected in this study (HR 1.07, NS). This discrepancy may be explained by the lower statistical power, Figure 3 Incidence rates of disability pension illustrating the combined effects of body mass index (BMI) and smoking status (n ¼ 45 920).…”

Adiposity Measures as Indicators of Metabolic Risk Factors in Adolescents

“…However, according to the %BF cut-offs recommended by McCarthy et al [19], 9 and 12% of the males were overfat and obese, respectively, and in females the corresponding percentages were 17.5 and 20.5%. This inconsistency between BMI and %BF has previously been documented [9,38] [39]. When using the WC cut-offs defined by the IDF, few were defined as having adverse levels, especially among the males.…”

Performance of body fat and body mass index cutoffs in elevated blood pressure screening among male children and adolescents

“…12 However, as is true for the BMI, the adoption of international reference tables seems to increase the proportion of falsenegative cases. [19][20][21] This is the case with the non age-adjusted cutoffs proposed by Williams et al, 8 where the higher cutoffs generated lower prevalence of obesity and, hence, higher specificity (true-negative cases). As mentioned above, outcome underestimation generates lower sensitivity (true-positive cases), that is, the capacity to correctly identify the outcome presence; therefore, both Taylor et al's 9 and McCarthy et al's 10 cutoffs, which presented higher outcome prevalence, also demonstrated slightly better accuracy in identifying the presence of EBP.…”