Bronchoprovocation testing

The effect of increasing the inhaled dose of methacholine in a healthy subject (red) and an asthmatic patient (blue). The provocative concentration is the amount of inhaled agonist required to drop the FEV₁ by 20 percent from the baseline (PC₂₀ FEV₁) and is much less in the asthmatic than in the normal subject: 0.8 mg/mL versus 20 mg/mL. In general, a PC₂₀ ≤8 mg/mL is consistent with asthma; and a PC₂₀ ​>16 mg/mL is considered a negative test. Thus, an increase in airway responsiveness is characterized by a decrease in the PC₂₀.