Asthma diagnosis and treatment – 1016. Is atopy in people aged 40 and over related to fixed airflow obstruction?

Background

The Tucson and Normative Ageing studies showed atopy was not related to airflow obstruction in later life, when known asthmatics were excluded. However these studies were based on pre-bronchodilator spirometry.

Aim

To examine independent associations between atopy and post-bronchodilator airflow obstruction in people aged 40 years and over.

Methods

We used data from the BOLD-Australia study. Persons aged 40 years and over were randomly selected from the electoral roll, either directly or via a two stage sampling procedure, in centres based in four Australian States. Spirometry was performed before and after administration of salbutamol 200 μg, according to a standardised protocol with careful attention to quality control. Subjects with post-bronchodilator FEV₁/FVC ratio < 0.7 were classified as GOLD stage 1 or higher. Subjects who also had FEV₁ < 80% predicted were classified as GOLD stage 2 or higher. Subjects who had a post-bronchodilator increase in FEV₁ > 12% of pre-bronchodilator value and > 200 ml were classified as “reversible”. Atopy was assessed by skin prick tests (SPTs) to house dust mites (D. pteronyssinus and D. farinae), cat, dog, cockroach, Alternaria, Aspergillus, rye grass and mixed grass pollens. Subjects with any allergen SPT ≥ 4 mm were classified as atopic.

Results

Post-bronchodilator spirometry and SPT data were available for 2,767 subjects (51.4% female, 12.1% aged ≥ 75). The prevalence of GOLD stage 1 or higher was 15.9%, the prevalence of GOLD stage 2 or higher was 6.8%, and 4.7% had bronchodilator reversibility. One in nine subjects self-reported current asthma and 50.5% had ever been smokers. The prevalence of atopy in this population was 42.7%.

The associations between atopy and airflow obstruction did not differ by self-reported asthma or smoking status (all interactions p > 0.2). However atopy was associated with GOLD stage 2 after adjustment for sex, self-reported current asthma and smoking status (OR=1.56, 95%CI 1.13-2.17). As expected, atopy was related to the presence of bronchodilator reversibility (OR=1.89, 95%CI 1.32-2.72).

Conclusions

The apparent association of atopy with fixed airflow obstruction using post-bronchodilator spirometry in people aged 40 years and over may be due to clinical heterogeneity.