Evaluating Canadian children: WHO, NHANES or what?

The 2006 World Health Organization (WHO) growth charts have been widely adopted by Canadian dieticians for growth monitoring of Canadian children rather than the National Health and Nutrition Examination Survey (NHANES III) reference data. It has been unclear as to which is the most appropriate.

We calculated height and weight z-scores of 3086 consecutive patients (1530 female, 49.6%) aged 0-5 years, attending outpatient clinics at a single tertiary care centre using reference data of the latest NHANES survey and the 2006 WHO growth charts. To address age dependency, data were stratified into age groups. Gender dependency was also investigated.

Using NHANES III reference intervals, medians of both height z-score (+0.24) and weight z-score (+0.32) were significantly non-zero. The WHO growth charts yielded medians of height z-score (-0.15) and weight z-score (+0.36) respectively, also significantly non-zero. When comparing both reference populations for the entire cohort, Canadian children had significantly different height z-scores whereas weight z-scores did not differ. Age classification revealed a significant age dependency with NHANES III charts yielding higher weight z-scores for up to 8 months and lower z-scores from 8 to 26 months. No significant differences were observed for older than 26 months. Throughout, height z-scores were significantly higher with NHANES III charts across all age groups, with a degree of overestimation higher in younger boys than older ones.

Our results reveal substantial differences between both reference populations and thus interpretation needs to be done with caution, especially when labelling results as abnormal.