Background: The methacholine challenge test is a common investigation used to identify airway hyperresponsiveness. There has been recent debate as to whether the airway effect is due to the concentration or the dose of methacholine.
Objective: To determine whether the airway response during a methacholine challenge test is due to the concentration or the dose of methacholine.
Methods: Ten subjects with stable, mild asthma were enrolled in this study. Two methacholine challenge tests, one with 30-second inhalations of methacholine and the other with two minute inhalations of methacholine, were performed on each subject in a random order on 2 days within a 1-week period at approximately the same time each day.
Results: The geometric mean 2-minute PC20 was 1.1 mg/mL and the geometric mean 30-second PC20 was 5.7 mg/mL, 5.2-fold greater than the mean 2-minute PC20. The paired t-test comparison of the 2-minute PC20 multiplied by 4 and the 30-second PC20 revealed no significant difference (P > .2).
Conclusions: The dose of methacholine is primarily responsible for the degree of bronchial response rather than the concentration.