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Background: Spirometry forms the foundation investigation for the diagnosis and monitoring of common pulmonary conditions. However, potential variation in spirometry interpretation for airflow obstruction may impact subsequent clinical management. Aim: To audit spirometry interpretation practices for airflow obstruction in Thoracic Society of Australia and New Zealand accredited laboratories. Methods: Thirty‐nine accredited complex lung function laboratories were invited to participate in an online survey. The survey enquired about demographics, definition of lower limit of normal range for spirometry parameters, spirometric parameters used for identifying airflow obstruction, spirometric definition of airflow obstruction, definition of significant bronchodilator response and chosen spirometry reference equations. Results: Thirty‐six laboratories provided complete responses (response rate, 92%). To define the lower limit of normal, 26 of 36 used the 5th percentile, 7 of 36 used a fixed cut‐off and 3 used other. Twenty‐nine laboratories utilised forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) as the sole parameter to identify airflow obstruction, 3 of 36 used FEV1/FVC and FEF25–75%, and 4 used other. To define airflow obstruction, 25 of 36 laboratories used FEV1/FVC < 5th percentile, 9 of 36 used a fixed cut‐off (FEV1/FVC < 0.7, 6/36; FEV1/FVC < 0.8, 2/36; FEV1/FVC < 0.75, 1/36) and 2 of 36 used other. Twenty‐six laboratories defined a significant bronchodilator response as an increase of at least 200 mL and 12% in FEV1 and/or FVC, 9 of 36 used ≥200 mL and ≥ 12% increase in FEV1 only, and 1 used other criteria. Reference equations utilised for interpretation of spirometry data included: Quanjer 2012 Global Lung Initiative (16/36), the third National Health and Nutritional Examination Survey (8/36), European Community of Coal and Steel (8/36) and other (4/36). Conclusions: Significant heterogeneity in spirometry interpretation for airflow obstruction exists across Australian and New Zealand accredited lung function laboratories. Lack of standardisation may translate into clinically appreciable differences for the diagnosis and management of common respiratory conditions. Ongoing discussion regarding formal standardisation is required. [ABSTRACT FROM AUTHOR]

BACKGROUND: Reversibility of obstructive lung disease is traditionally defined by changes in FEV1 or FVC in response to bronchodilators. These may not fully reflect changes due to a reduction in hyperinflation or air-trapping, which have important clinical implications. To date, only a handful of studies have examined bronchodilators' effect on lung volumes. The authors sought to better characterize the response of residual volume and total lung capacity to bronchodilators. METHODS: Responsiveness of residual volume and total lung capacity to bronchodilators was assessed with a retrospective analysis of pulmonary function tests of 965 subjects with obstructive lung disease as defined by the lower limit of normal based on National Health and Nutritional Examination Survey III prediction equations. RESULTS: A statistically significant number of subjects demonstrated response to bronchodilators in their residual volume independent of response defined by FEV1 or FVC, the American Thoracic Society and European Respiratory Society criteria. Reduced residual volume weakly correlated with response to FEV1 and to FVC. No statistically significant correlation was found between total lung capacity and either FEV1 or FVC. CONCLUSIONS: A significant number of subjects classified as being nonresponsive based on spirometry have reversible residual volumes. Subjects whose residual volumes improve in response to bronchodilators represent an important subgroup of those with obstructive lung disease. The identification of this subgroup better characterizes the heterogeneity of obstructive lung disease. The clinical importance of these findings is unclear but warrants further study. [ABSTRACT FROM AUTHOR]