Applying the WHO instead of CDC growth charts may double obesity rates

Abeer Yasin, Guido Filler

Department of Paediatrics, Division of Paediatric Nephrology, Children’s Hospital, London Health Sciences Centre, London, Canada.

DOI: 10.4236/ojped.2013.32025                

Abstract

Aims: This study compares the WHO (2007) and the National Health Examination Survey (NHANES III) reference intervals and investigates the differences when applied on a Canadian cohort of older children and adolescents. Methods: We calculated height, weight and BMI z-scores of 4375 consecutive patients (1993 female, 45.6%) aged 5 - 20 years attending outpatient clinics at a single tertiary care centre using reference data of the latest NHANES (III) survey and the WHO (2007) growth charts. To address age dependency, data was stratified into age groups. Results: Using the NHANES III reference intervals, medians of weight (+0.46), height (+0.29) and BMI z-scores (+0.46) were significantly non-zero. The WHO (2007) growth charts yielded medians of +2.05, +0.32, +0.53 for weight, height and BMI z-scores respectively, all significantly non-zero. When comparing both growth charts, Canadian children had significantly different weight and BMI z-scores (p < 0.0001) with WHO growth charts whereas height z-score did not differ. Obesity rates (BMI z-score > 95th percentile) doubled from 8.6% to 16.0%. A significant age dependency was observed with higher WHO (2007) weight z-scores (>7 years) and higher BMI z-scores (7 to 13 years) and no significant difference was observed for height z-scores across all age groups. Gender differences were observed for weight z-scores (>9 years) and BMI (males: 9 - 11 years, p = 0.0118; 11 - 13 years, p = 0.0069) whereas no significant difference was found in height z-scores across all age groups. Conclusion: Our results reveal substantial differences between both reference populations and thus interpretation needs be done with caution, especially when labelling results as abnormal.

Keywords

WHO; NHANES; Height z-Score; Weight z-Score; BMI z-Score; Bland & Altman Agreement; Obesity Rates

Conflicts of Interest

The authors declare no conflicts of interest.

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