methacholinetest

Methacholine test is a diagnostic procedure used primarily to assess airway hyperreactivity, commonly associated with asthma. The test involves inhaling a substance called methacholine, a cholinergic agonist that mimics the effects of nervous system stimulation on the airway smooth muscles. When inhaled, methacholine causes bronchoconstriction, or narrowing of the airways, which can be measured through lung function tests.

The procedure is typically performed in a clinical setting. It begins with baseline spirometry, a test of lung function, to determine the patient's normal airway status. The patient then inhales increasing concentrations of methacholine aerosolized in a controlled manner. After each dose, lung function is reassessed. A significant decrease—usually a 20% reduction in forced expiratory volume in one second (FEV1)—indicates airway hyperresponsiveness.

The methacholine challenge test is valued for its specificity in diagnosing asthma, especially in cases where symptoms are intermittent or non-specific. It helps distinguish asthma from other respiratory conditions with similar clinical presentations. However, the test is contraindicated in individuals with certain cardiovascular issues, severe airflow obstruction, or recent respiratory infections.

Though generally safe, the test carries some risks such as bronchospasm or coughing. Therefore, it must be conducted under medical supervision with emergency equipment available. The results assist clinicians in confirming or ruling out asthma and in evaluating the severity of airway sensitivity, guiding appropriate treatment strategies.