Methacholine Test

The methacholine test is a diagnostic examination used to detect asthma, especially when symptoms are mild or irregular. Methacholine is a substance that causes narrowing of the airways (bronchospasm) in people with asthma, but not in healthy individuals. The test is performed by having a person inhale increasing amounts of methacholine. After each inhalation, it is measured how much air a person can exhale at once. If the amount of air a person can exhale is reduced by a certain percentage, the test is positive for asthma.