Background: Asthma is a heterogeneous disease with a wide range of clinical phenotypes, not all of which may be encompassed in the subjects included in randomised controlled trials (RCTs). This makes it difficult for clinicians to know to what extent the evidence derived from RCTs applies to a given patient. Aim: To calculate the proportion of individuals with asthma who would have been eligible for the major asthma RCTs from the data of a random community survey of respiratory health. Methods: A postal survey was sent to 3500 randomly selected individuals aged 25-75 years. Respondents were invited to complete a detailed respiratory questionnaire and pulmonary function testing. Participants with current asthma were assessed against the eligibility criteria of the 17 major asthma RCTs cited in the Global Initiative for Asthma (GINA) guidelines. Findings: A total of 749 participants completed the full survey, of whom 179 had current asthma. A median 4% of participants with current asthma (range 0-36%) met the eligibility criteria for the included RCTs. A median 6% (range 0-43%) of participants with current asthma on treatment met the eligibility criteria. Interpretation: This study shows that the major asthma RCTs on which the GINA guidelines are based may have limited external validity as they have been performed on highly selected patient populations. Most of the participants with current asthma on treatment in the community would not have been eligible for these RCTs.

The reference ranges presented may be used to assist in the interpretation of Fe(NO) measurements in white adults.

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Airways disease is currently classified using diagnostic labels such as asthma, chronic bronchitis and emphysema. The current definitions of these classifications may not reflect the phenotypes of airways disease in the community, which may have differing disease processes, clinical features or responses to treatment. The aim of the present study was to use cluster analysis to explore clinical phenotypes in a community population with airways disease.A random population sample of 25-75-yr-old adults underwent detailed investigation, including a clinical questionnaire, pulmonary function tests, nitric oxide measurements, blood tests and chest computed tomography. Cluster analysis was performed on the subgroup with current respiratory symptoms or obstructive spirometric results.Subjects with a complete dataset (n5175) were included in the cluster analysis. Five clusters were identified with the following characteristics: cluster 1: severe and markedly variable airflow obstruction with features of atopic asthma, chronic bronchitis and emphysema; cluster 2: features of emphysema alone; cluster 3: atopic asthma with eosinophilic airways inflammation; cluster 4: mild airflow obstruction without other dominant phenotypic features; and cluster 5: chronic bronchitis in nonsmokers.Five distinct clinical phenotypes of airflow obstruction were identified. If confirmed in other populations, these findings may form the basis of a modified taxonomy for the disorders of airways obstruction.

Background: Chronic obstructive pulmonary disease (COPD) encompasses a group of disorders characterised by the presence of incompletely reversible airflow obstruction with overlapping subsets of different phenotypes including chronic bronchitis, emphysema or asthma. The aim of this study was to determine the proportion of adult subjects aged .50 years within each phenotypic subgroup of COPD, defined as a post-bronchodilator ratio of forced expiratory volume in 1 s/forced vital capacity (FEV 1 /FVC) ,0.7, in accordance with current international guidelines. Methods: Adults aged .50 years derived from a random population-based survey undertook detailed questionnaires, pulmonary function tests and chest CT scans. The proportion of subjects in each of 16 distinct phenotypes was determined based on combinations of chronic bronchitis, emphysema and asthma, with and without incompletely reversible airflow obstruction defined by a post-bronchodilator FEV 1 /FVC ratio of 0.7. Results: A total of 469 subjects completed the investigative modules, 96 of whom (20.5%) had COPD.Diagrams were constructed to demonstrate the relative proportions of the phenotypic subgroups in subjects with and without COPD. 18/96 subjects with COPD (19%) had the classical phenotypes of chronic bronchitis and/or emphysema but no asthma; asthma was the predominant COPD phenotype, being present in 53/96 (55%). When COPD was defined as a post-bronchodilator FEV 1 /FVC less than the lower limit of normal, there were one-third fewer subjects with COPD and a smaller proportion without a defined emphysema, chronic bronchitis or asthma phenotype. Conclusion: This study provides proportional classifications of the phenotypic subgroups of COPD which can be used as the basis for further research into the pathogenesis and treatment of this heterogeneous disorder.