This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstructive Lung Disease, Subject name: Pathology
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? 
Select and explain. 
A. Absence of peripheral blood eosinophilia, B. Negative allergy skin tests, C. Negative methacholine challenge, D. Normal total serum IgE level
C: Negative methacholine challenge
Answer: C: Negative methacholine challenge 
Explanation: 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.