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©2013 UpToDate ® Print Email Bronchoprovocation testing The effect of increasing the inhaled dose of histamine or 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 versus 20 mg/mL). An increase in responsiveness is characterized by a decrease in the PC20.