A positive bronchial provocation test (methacholine challenge) is defined as what percent decrease in FEV1?

A positive bronchial provocation test (methacholine challenge) is defined as what percent decrease in FEV1?

• A. 20% decrease in FEV1
• B. 5% decrease in FEV1
• C. 10% decrease in FEV1
• D. 40% decrease in FEV1

Answer: (A)

Bronchial provocation tests measure airway hyperresponsiveness by exposing the airways to a bronchoconstrictor (methacholine) and tracking how much FEV1 falls from the baseline. In reactive airways, even small doses cause a notable constriction, so the test uses the percent decline in FEV1 to define positivity. The standard threshold is a 20% decrease in FEV1 from baseline, which is why a 20% drop is the correct criterion. This cutoff (often expressed as the concentration causing a 20% fall, or PC20) provides a balance between sensitivity and specificity. Smaller declines would be less specific and could be seen in normal variation, while a much larger decline would not be the customary threshold for positivity. A positive result indicates bronchial hyperresponsiveness, commonly associated with asthma.

Bronchial provocation tests measure airway hyperresponsiveness by exposing the airways to a bronchoconstrictor (methacholine) and tracking how much FEV1 falls from the baseline. In reactive airways, even small doses cause a notable constriction, so the test uses the percent decline in FEV1 to define positivity. The standard threshold is a 20% decrease in FEV1 from baseline, which is why a 20% drop is the correct criterion. This cutoff (often expressed as the concentration causing a 20% fall, or PC20) provides a balance between sensitivity and specificity. Smaller declines would be less specific and could be seen in normal variation, while a much larger decline would not be the customary threshold for positivity. A positive result indicates bronchial hyperresponsiveness, commonly associated with asthma.