Methacholine Challenge

The Methacholine Challenge Test is a method of diagnosing asthma, especially in adults where their medical history of asthma (e.g. childhood asthma) is uncertain. When methacholine is administered to an individual with reactive airway disease, bronchoconstriction will occur, which is detected through pulmonary function testing. Essentially, the methacholine chemically induces an asthma attack.

Obviously if an individual has well-documented asthma, you're not going to give them a Methacholine Challenge Test. It would be akin to giving someone with a known allergy to peanuts a Snicker's Bar to "see what happens".

The Methacholine Challenge test has a sensitivity and specificity of approximately 90%, i.e. it is fairly accurate. However, it still means that 1 in 10 individuals WITH asthma will not be detected through Methacholine Challenge testing (what is known as a "false negative"), and that 1 in 10 individuals who do NOT have asthma will have a positive Methacholine Challenge test.

The validity of an individual Methacholine Challenge test can be affected by numerous factors, including cigarette smoke, environmental pollution, caffeine, chocolate, anything containing ephedrine, and of course any medication to treat asthma.

I should also mention that, although rare, life-threatening reactions have occured with Methacholine Challenge Testing. The test itself must be conducted in a setting where any severe adverse reaction can be treated immediately, e.g. oxygen, Epinephrine (Adrenalin), etc., and the ability to handle a full-blown cardiopulmonary resuscitation. It is for this reason that many civilian centers use alternate testing methods, e.g. PFT "stress testing" for the diagnosis of exercise-induced asthma.