• Nicolette R Holt, Bruce R Thompson, Belinda Miller, and Brigitte M Borg.
• Department of Respiratory Medicine, The Alfred Hospital, Melbourne, Victoria, Australia.
• Intern Med J. 2019 Jan 1; 49 (1): 41-47.

BackgroundSpirometry 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.AimTo audit spirometry interpretation practices for airflow obstruction in Thoracic Society of Australia and New Zealand accredited laboratories.MethodsThirty-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.ResultsThirty-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).ConclusionsSignificant 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.© 2018 Royal Australasian College of Physicians.

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