Atopy in people aged 40 years and over: Relation to airflow limitation.

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 weal to common aeroallergens ≥4 mm. 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 prevalence of atopy, ever diagnosed asthma and post-bronchodilator airflow obstruction was 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.