Metacholine challenge test

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This is the best test for statistically distinguishing asthmatics from non-asthmatics. 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 metacholine test, anyone who appears to have asthma clinically, and who responds to asthma treatment, should not have asthma treatment with held because he passes a metacholine challenge.

The test is physically demanding, and the results can be affected by muscular weakness or exhaustion. The maneuver the patient performs is called spirometry, and can cause a sharp spike in blood pressure while being performed. Metacholine can, sometimes, stimulate the upper airway sufficiently to cause violent coughing. This can make spirometry difficult or impossible.