Methods: The patients who were performed both methacholine challenge tests and pulmonary function tests with bronchodilator for suspected asthma from 2002 to 2013 were selected and the results of the tests from order communication system were reviewed. Diagnostic criteria of asthma were defined by one or more of following: the provocative concentration of methacholine causing a 20% fall in FEV1 from baseline (PC20) or extrapolated PC20 less than or equal to 25 mg/mL (1st criterion), an increase in FEV1 of >12% and >200 mL from baseline after 200 μg of salbutamol (2nd criterion), an increase in FEV1 of >12% and >200 mL from baseline after anti-inflammatory treatment or a variation in FEV1 of >12% and >200 mL between visits within 1 year and FEV1/FVC ≤0.75 at least once (3rd criterion). FEV1 and/or FVC bronchodilator response was defined as increases in FEV1 and/or FVC >12% and >200 mL from baseline after 200 μg of salbutamol. The sensitivity and the specificity of the FEV1 and/or FVC bronchodilator response for asthma diagnosis were calculated.
Results: A total 2616 pulmonary function tests with salbutamol and 1496 methacholine challenge tests in 1434 patients from 12 to 89 years old were analyzed. The diagnostic criteria of asthma were satisfied in 874 (60.9%) patients. Among them, numbers of patients who met each criterion were 831 (95.1%) for 1st criterion, 120 (13.7%) for 2nd criterion, 181 (20.7%) for 3rd criterion. Among 1834 pulmonary function tests in the asthma patients, 191 (sensitivity 10.4%) tests showed positive FEV1 and/or FVC bronchodilator response, while only 152 (sensitivity 8.3%) tests showed positive FEV1 bronchodilator response. False positive results in FEV1 and/or FVC bronchodilator response were shown in only 3 of 782 pulmonary function tests of patients without asthma (specificity 99.6%). The false positive results were shown in 3 different patients. Among them 2 patients were real asthma patients according to the results of other pulmonary function tests which were not evaluated in this study and the other patient had history of asthma.
Conclusions: An increases in FEV1 and/or FVC >12% and >200 mL from baseline after bronchodilators could have also diagnostic value for asthma.