Bronchial challenge test

There are some respiratory diseases such as exercise-induced asthma that are not apparent unless the patient is exposed to some sort of trigger, such as a chemical irritant, an allergen, cold or dry air, or rigorous exercise. To diagnose these conditions, a bronchial challenge test is performed. This is to discover which environmental conditions may triggering the bronchospasm, or sudden contraction of the bronchioles, and subsequent breathing problems. This test also helps determine the extent of the reaction.

As part of this test, the patient's medical history is taken and possible triggers are discussed. Spirometry tests are taken. The patient is exposed to whatever triggers the breathing problem, under controlled conditions. Spirometry tests are again taken, and compared with the earlier results.

In such tests, pharmaceutical agents such as methacholine or histamine may be used.

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 is an important part in diagnosing asthma versus COPD.