Methacholine challenge test

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A methacholine challenge test is a medical test used to assist in the diagnosis of asthma. The patient breathes in nebulized methacholine. This provokes narrowing of the airways (bronchoconstriction). This is detected when the patient performs spirometry. People with asthma react to lower doses of inhaled methacholine.

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.). Regardless of the results of a methacholine test, anyone who appears to have asthma clinically, and who responds to asthma treatment, should have asthma treatment. Asthma treatment should not be withheld in such a patient who passed a methacholine challenge.

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

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The following article is not written by a medical professional and some of the information may be incorect. About.com explanation of the procedure, and the purpose in relation to U.S. Military enlistment