Bronchial Provocation Methacholine PC20

A 24-year-old medical student presents with a 6-month history of intermittent dry cough, chest tightness during exercise, and nocturnal wheezing twice per week. Baseline spirometry shows FEV1 3.2 L (98% predicted), FVC 3.8 L (95% predicted), and FEV1/FVC 0.84—all normal. Methacholine bronchoprovocation challenge is performed using doubling concentrations (0.03–16 mg/mL). At 2.0 mg/mL, her FEV1 drops to 78% of baseline, representing a 22% decline. The test is terminated and log-linear interpolation calculates the value marked **C** in the diagram as 1.7 mg/mL. Which of the following best describes the clinical significance of this finding?