Body mass index cutoff point estimation as obesity diagnostic criteria in Down syndrome adolescents / Estimación del punto de corte del índice de masa corporal como criterio diagnóstico de obesidad en adolescentes con síndrome de Down

Introduction: Adolescents with Down syndrome (DS) show high rate of overweight and tend to accumulate high amount of fat compared to the same people without the syndrome. Objective: To estimate the cutoff point of the Body Mass Index (BMI) for the diagnosis of obesity in adolescents with DS according to different references for BMI in relation to the percentage of body fat (%BF) measured by dual-energy X-ray absorptiometry (DXA). Methods: The sample was composed of 34 adolescents with DS (aged: 10 to 17 years old). BMI was evaluated according to the references of the International Obesity Task Force (IOTF), the World Health Organization (WHO) for the general population, and Myrelid et al. and Styles et al. for people with DS. The %BF was assessed by whole body DXA and classified according to National Health And Nutrition Examination Survey (NHANES, 2011). Results: The boys were significantly taller than the girls and this %BF higher than boys. All references who have used BMI to assess obesity was positively associated with %BF measured by DXA in the diagnosis of obesity. Using the ROC curve in relation to %BF by DXA, all references showed high sensitivity, but the z-score of BMI by WHO showed better specificity, with the value of the accuracy of 0.82 for the cutoff point above 2.14. Conclusions: All the references used for the diagnosis of obesity were associated with %BF measured by DXA, and the cutoff point of z-scores above 2.14 by WHO showed better specificity (AU)

Introducción: adolescentes con síndrome de Down (SD) muestran alta tasa de sobrepeso y tienden a acumular gran cantidad de grasa en comparación con los adolescentes sin el síndrome. Objetivo: estimar el punto de corte del índice de masa corporal (IMC) para el diagnóstico de obesidad en adolescentes con SD de acuerdo con las diferentes referencias para el IMC en relación con el porcentaje de grasa corporal (%GC) obtenido por el absorciometría con rayos X de doble energía (DXA). Métodos: la muestra se compone de 34 adolescentes con SD (10 a 17 años). El IMC se evaluó de acuerdo con las referencias de la International Obesity Task Force (IOTF), Organización Mundial de la Salud (OMS) para la población general, y Myrelid et al. y Estyles et al. para personas con SD. El %GC fue evaluado por DXA y clasificado según NHANES (2011). Resultados: los niños fueron significativamente más altos que las niñas, y estas con mayor %GC que los niños. Todas las referencias que han utilizado el IMC se asociaron positivamente con el %GC medido por DXA en el diagnóstico de la obesidad. Utilizando la curva ROC en relación con %GC por DXA todas las referencias mostraron alta sensibilidad, pero el score-z del IMC por la OMS mostró mejor especificidad, con el valor de exactitud de 0,82 para el punto de corte por encima de 2,14. Conclusiones: todas las referencias utilizadas para el diagnóstico de obesidad se asociaron con el %GC medido por DXA, y el punto de corte del score-z por encima de 2,14 por la OMS mostró mejor especificidad (AU)

Accuracy of Body Mass Index Cutoffs for Classifying Obesity in Chilean Children and Adolescents.

OBJECTIVE: To determine the accuracy of two international Body Mass Index (BMI) cut-offs for classifying obesity compared to the percentage of fat mass (%FM) assessed by Dual-Energy X-ray Absorptiometry (DXA) in a Chilean sample of children and adolescents; MATERIAL AND METHODS: The subjects studied included 280 children and adolescents (125 girls and 155 boys) aged 8 to 17 years. Weight and height were measured. The BMI was calculated. Two international references (IOFT and WHO) were used as cut-off points. The %FM was assessed by DXA. The receiver operating characteristic (ROC) curve was used to assess the performance of BMI in detecting obesity on the basis of %FM; RESULTS: A high correlation was observed between the %FM measured by the DXA and the Z-scores of IOTF and WHO scores in the Chilean adolescents separated by sex (r = 0.78-0.80). Differences occurred in both references (IOFT and WHO) in relation to the criteria (p < 0.001). Both references demonstrated a good ability to predict sensitivity (between 84% and 93%) and specificity (between 83% and 88%) in both sexes of children and adolescents; CONCLUSIONS: A high correlation was observed between the Z-score of the BMI with the percentage of fat determined by the DXA. Despite this, the classifications using the different BMI cut-off points showed discrepancies. This suggests that the cut-off points selected to predict obesity in this sample should be viewed with caution.