Confirmation of asthma in an era of overdiagnosis.

It was recently shown that 30% of adults with a physician diagnosis of asthma did not have asthma when objectively assessed using a four-step algorithm involving serial spirometry, bronchial challenge testing and subsequent tapering of asthma medications. The objective of the present study was to determine how many steps in the algorithm were required in order to confirm asthma, and whether any patient-related variables were associated with earlier asthma confirmation. A total of 540 subjects with a previous physician diagnosis of asthma were randomly recruited from the community. The number of subjects confirmed with asthma at each study visit was calculated. Regression analysis was used to determine variables associated with earlier asthma confirmation. Of the 499 subjects who completed the diagnostic algorithm, 346 (69%) had asthma confirmed and 150 (30%) had asthma excluded. Of subjects in whom asthma was confirmed, including those using regular asthma controlling medications, >90% were confirmed with only one or two study visits, by either pre- and post-bronchodilator spirometry or a single bronchial challenge test. Only 46 (9%) out of 499 subjects required tapering of asthma medications and repeated bronchial challenge tests for exclusion or confirmation of asthma. Lower forced expiratory volume in 1 s and younger age were associated with earlier asthma confirmation. For the majority with a previous physician diagnosis of asthma, only pre- and post-bronchodilator spirometry and a single methacholine challenge test are required in order to confirm asthma.