Abstract
Background
Previous studies have reached conflicting conclusions about the role of atopy as a risk factor for COPD. In part, this is attributable to variation in the definitions of airflow limitation and the treatment of people with asthma.
Objective
To establish whether there is any independent association between atopy and post-bronchodilator airflow limitation in the general population aged 40 years and over.
Methods
A cross-sectional survey was conducted in a general population sample of 2415 people aged 40 years and over in Australia. A history of ever being diagnosed with asthma was elicited by questionnaire. Atopy was defined as any skin prick test wheal to common aero-allergens ≥4mm. Airflow limitation was defined as post-bronchodilator spirometric (FEV1/FVC) ratio < lower limit of normal. Analyses were adjusted for potential confounding due to age, sex, smoking, race and socio-economic status.
Results
The prevalences of atopy, ever diagnosed asthma and post-bronchodilator airflow obstruction were 44.8%, 19.3% and 7.5%, respectively. In the population as a whole, atopy was associated with lower FEV₁ (adjusted difference -0.068L, 95% confidence interval(CI) -0.104 to -0.032), FVC (adj. difference -0.043L, 95%CI -0.086 to -0.0009) and post-bronchodilator FEV₁/FVC ratio (adj. difference -0.011, 95%CI -0.017 to -0.0055). The effect of atopy on lung function was no longer apparent when participants who reported ever diagnosed asthma were excluded (FEV₁ -0.011L, [95% CI -0.05 to 0.028L], FVC -0.012L [95% CI -0.060 to 0.036] and FEV₁/FVC ratio -0.0012 [95% CI -0.0072 to 0.0047L]).
Conclusion and Clinical Relevance
The apparent association between atopy and post-bronchodilator airflow limitation in the general population appears to be explained by the association between atopy and having ever diagnosed asthma and the effect of asthma on lung function.
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