Methacholine Challenge Test

Methacholine challenge tests are a lung function test for asthma and are more commonly used in adults than in children. It might be performed if your symptoms and screening spirometry do not clearly or convincingly establish a diagnosis of asthma. Methacholine is an agent that, when inhaled, causes the airways to spasm (contract involuntarily) and narrow if asthma is present. During this test, you inhale increasing amounts of methacholine aerosol mist before and after spirometry. The methacholine test is considered positive, meaning asthma is present, if the lung function drops by at least 20%. A bronchodilator is always given at the end of the test to reverse the effects of the methacholine.