A 12 year-old boy develops intermittent shoness of breath over the past 6 months. He is not on any medications and has no significant family history. The vitals are within normal limits and the lungs are clear to auscultation. Lung function tests reveal a FEV1/FVC ratio of 82%. Which of the following would be most helpful in excluding a diagnosis of asthma in this patient?
In pts with asthma the airways are Hyper-responsive and administration of methacholine causes more spasm- METHACHOLINE CHALLENGE TEST. If patient has asthma, it will fuher cause deterioration. So this test is useful for diagnosis.