View Abstract

A1892 - Obstructive Lung Diseases in Australian Adults: A Latent Class Analysis
Author Block: E. Guevara-Rattray1, F. Garden2, H. K. Reddel3, A. L. James4, B. Toelle3, G. B. Marks2; 1South Western Sydney Clinical School, University of New South Wales, Liverpool, Australia, 2Ingham Institute of Applied Medical Research, University of New South Wales, Liverpool, Australia, 3Woolcock Inst of Medical Research, Glebe, Australia, 4Sir Charles Gairdner Hosp, Nedlands, Australia.
Introduction: Existing phenotypic classifications of obstructive lung disease are largely historical in their origins and are demonstrably not fit for purpose in describing a heterogeneous disease. An unsupervised, data driven approach would identify real-world phenotypes. Aims: To describe phenotypes of obstructive lung disease in people aged 40 years and over. Methods: A random sample of the population aged 40 and over living in Sydney and Busselton (n=827) completed questionnaires, spirometry, exhaled nitric oxide (FeNO) and skin prick tests. Latent class analysis was used to identify classes and assign a probability of class membership to individuals. Our model included respiratory symptoms (wheeze, cough and dyspnea score), spirometric lung function (post-bronchodilator FVC, post-bronchodilator FEV1/FVC and absolute change in FEV1 after administration of bronchodilator) and FeNO. Spirometric lung volumes were adjusted for height and sex. The relation of class membership to smoking history, asthma diagnosis and atopic status was assessed. Results: The following five class solution was identified as the best fitting model: (1) ‘Asymptomatic with normal spirometric function’ represented 73.5% of the population, (2) ‘Symptomatic with non-reversible airflow limitation (COPD)’ (2.4%), (3) ‘Cough with normal spirometric function (19.1%), (4) ‘Dyspnoea with small lungs’ (4.1%) and (5) ‘Bronchodilator reversibility with elevated FeNO (Eosinophilic asthma)’ (0.8%). The highest proportion of ever-smokers was in class 2 (65%, including 45% with ≥ 20 pack-years). Those in Class 5 appeared to have significant asthma yet only 14.3% were using inhaled corticosteroids (ICS). Among those in Class 3 ‘Cough with normal spirometric function’, 20% had been diagnosed with asthma during their lifetime and 16.5% were using ICS. Only Class 5 (“Bronchodilator reversibility with elevated FeNO (Eosinophilic asthma)”) was strongly linked to atopy. Conclusion: Latent class analysis allowed us to describe obstructive lung disease in the general population. Classic “COPD” (Class 2) and “Eosinophilic asthma” (Class 5) are uncommon, but lung function was assessed only once. Cough with normal lung function is common and some people who complain of breathlessness have small lungs without physiological evidence of airways disease.