Bronchial challenge test

A bronchial challenge test is a medical test used to assist in the diagnosis of asthma. The patient breathes in nebulized drug: either methacholine or histamine. Thus the test may also be called a methacholine challenge test or histamine challenge test respectively. The drug provokes narrowing of the airways (bronchoconstriction). This is detected when the patient performs spirometry. People with asthma react to lower doses.

Sometimes, to assess the reversibility of a particular condition, a bronchodilator is administered before performing another round of tests for comparison. This is commonly referred to as a reversibility test, or a post bronchodilator test (post BD), and may help in distinguishing asthma from chronic obstructive pulmonary disease.

However it is possible to have false negatives, and false positives on this test. Asthma can also be temporary, due to an exposure to noxious stimuli (smoke inhalation, etc.).

The test is physically demanding, and the results can be affected by muscular weakness or exhaustion. The inhaled drug can stimulate the upper airway sufficiently to cause violent coughing. This can make spirometry difficult or impossible.