Airway Hyperresponsiveness in Asthma: Measurement and Clinical Relevance.

Airway hyperresponsiveness is a characteristic feature of asthma, and its measurement is an important tool in its diagnosis. With a few caveats, methacholine bronchial provocation by a 2-minute tidal breathing method is highly sensitive; a negative test result (PC > 16 mg/mL, PD > 400 μg) rules out current asthma with reasonable certainty. A PC value of less than 1 mg/mL/PD value of less than 25 μg is highly specific (ie, diagnostic) but quite insensitive for asthma.