Role of Methacholine PC20 in FEF25-75% for the Diagnosis of Bronchial Asthma

Background: The methacholine bronchial provocation test is a useful tool for evaluating asthma in patients with normal or near normal baseline lung function. However, the sensitivity of this test is 82∼92% at most. The purpose of this study is to evaluate the clinical usefulness of FEF25-75% in identification of airway hyperresponsiveness in patients with suspected asthmatic symptoms. Methods: One hundred twenty-five patients who experienced cough and wheezing within one week prior to their visiting the clinic were enrolled. Results: Sixty-four subjects showed no significant reduction of FEV1 or FEF25-75% on the methacholine bronchial provocation test (Group I). In 24 patients, FEF25-75% fell more than 20% from baseline without a 20% fall of FEV1 during methacholine challenge (Group II). All patients who had more than 20% fall of FEV1 (n=37) also showed more than 20% of reduction in FEF25-75% (Group III). Baseline FEV1/FVC (%) and FEF25-75% (L) were higher in group II than group III (81.51±1.56% vs. 75.02±1.60%, p<0.001, 3.25±0.21 L vs. 2.45±0.21 L, p=0.013, respectively). Group II had greater reductions of both FEV1 and FEF25-75% than group I at 25 mg/mL of methacholine (p<0.001). The provocative concentration of methacholine causing a 20% fall in FEF25-75% in group II was about three-fold higher than that in group III. Conclusion: A 20% fall of FEF25-75% by methacholine provocation can be more sensitive indicator for detecting a milder form of airway hyperresponsiveness than FEV1 criteria.