Final answer:
The methacholine challenge test is used to assess airway hyperresponsiveness, which helps diagnose asthma. A positive result, indicated by a 20% or more decrease in FEV1 after methacholine inhalation, suggests asthma. The test findings are considered alongside the patient's clinical history for a conclusive diagnosis.
Step-by-step explanation:
Understanding the Methacholine Challenge Test
A methacholine challenge test is a diagnostic procedure used to evaluate airway hyperresponsiveness, which can help in diagnosing conditions like asthma. The test involves inhalation of methacholine, a substance that can cause narrowing of the airways. By monitoring the patient's lung function before and after methacholine inhalation, healthcare providers can establish the degree of airway responsiveness.
Conclusions and Findings
If a patient's airway narrows significantly after inhaling methacholine, the test is considered positive, indicating a higher likelihood of asthma or airway hyperreactivity. The degree of narrowing is measured by a decrease in the Forced Expiratory Volume in one second (FEV1). Generally, a fall in FEV1 of 20% or more from the baseline is considered a positive result. However, a negative test does not completely exclude asthma, but it makes it less likely, especially if the symptoms are not typical of asthma.
The findings from a methacholine challenge test are used in conjunction with clinical history and other diagnostic tests to make a comprehensive asthma diagnosis.