Bronchodilator Reversibility As A Diagnostic Test for Adult Asthma: Findings from the Population-Based Tasmanian Longitudinal Health Study.

Introduction. Bronchodilator reversibility (BDR) is often used as a diagnostic test for adult asthma. However, there has been limited assessment of its diagnostic utility. Aim. To determine the discriminatory accuracy of currently used BDR cut-offs in the context of current asthma and asthma-COPD overlap (ACO) in middle-aged Australians. Methods. The Tasmanian Longitudinal Health Study (TAHS) is a population-based cohort first studied in 1968 (n = 8,583). In 2012, participants completed respiratory questionnaires and spirometry (n = 3,609; mean age 53 years). Current asthma was defined as having a history of doctor-diagnosed asthma with asthma-related symptoms, healthcare or medication utilisation in the last one month. Receiver operating characteristic (ROC) curves were fitted for current asthma and ACO using continuous BDR measurements. Diagnostic parameters were calculated for different categorical cut-offs. Results. Area under the ROC curve (AUC) was highest when BDR was expressed as change in FEV1 as a percentage of initial FEV1, as compared with predicted FEV1. The corresponding AUC was 59% (95% CI 54-64%) for current asthma and 87% (95%CI 81-93%) for ACO. Of the cut-offs examined, the European Respiratory Society/American Thoracic Society (ERS/ATS) threshold (>=12% from baseline and >= 200 ml) was assessed as providing the best balance between positive and negative likelihood ratios, with corresponding sensitivities and specificities of 9% and 96% for current asthma, and 47% and 97% respectively for ACO. Conclusion. Current recommended cut-offs can assist with ruling in, but are poor at ruling out adult asthma, with an optimal threshold of >=12% and >= 200 ml from baseline. BDR was more useful as diagnostic test in those with co-existent post-bronchodilator airflow obstruction (ACO).