How do Cormic Index profiles contribute to differences in spirometry values between White and First Nations Australian children?

Abstract

Background: Spirometry values of First Nations Australian children are lower than White children. One explanation relates to differences in the sitting-height/ standing-height ratio (Cormic Index), as this accounts for up to half the observed differences in spirometry values between White children and other ethnicities. We investigated whether the Cormic Index of First Nations children differs from White children and if this explains the lower spirometry values of First Nations children. Methods: First Nations children (n = 619) aged 8-16 years were recruited from nine Queensland communities. Their spirometry and Cormic Index data were compared to that of White children (n = 907) aged 8-16 years from the NHANES III dataset.Results: FEV 1 and FVC of First Nations children was 8% lower for children aged 8-11.9 years and 9%-10% lower for children aged 12-16 years. The Cormic Index was statistically lower in the First Nations 8-11.9 years group (median = 0.515, interquartile range [IQR]: 0.506-0.525) compared with White children (0.519, IQR: 0.511-0.527), and this difference was greater in the 12-16 years group (0.505, IQR: 0.492-0.516; 0.520, IQR: 0.510-0.529). Adjusting for age, sex, and standing height, lower Cormic Index of First Nations children accounts for 14% (95% confidence interval [CI]: 7%-21%) of FEV 1 and 15% (95% CI: 8%-21%) of FVC differences in the younger group, and 26% (95% CI: 16%-37%) of FEV 1 and 31% (95% CI: 19%-42%) of FVC differences in the older group. Conclusion: Ethnic differences in Cormic Index partly account for why healthy First Nations Australian children have lower spirometry values than White children. As childhood spirometry values impact adult health, other contributing factors require attention.

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“…A further consideration of our cross-sectional study was that we Finally, borderline low spirometry findings may well have been normal if adjusted for the lower Cormic Index observed in Aboriginal children. 27 However, the presence of a respiratory physician on the study team facilitated interpretation of results, for example, where a borderline restrictive spirometry curve was found in the absence of abnormal symptoms or physical findings children were classified as healthy.…”

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“…Collaro et al 47 The mean FVC, FEV 1 , and forced expiratory flow between 25% and 75% of FVC (FEF 25-75 ) fit the predicted value based on GLI reference equation for Northeast Asians. However, the observed variance was slightly greater than the predicted, resulting in a high lower limit of normal and possible overdiagnosis of lung function impairment.…”

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