A 49-year-old woman is evaluated for a 4-month history of dry cough, which began 4 months ago when she noted a paroxysmal onset of persistent coughing spells that make it difficult to carry on a conversation. She was initially diagnosed with allergic rhinitis and was started on a glucocorticoid nasal inhaler with no improvement. Medical history is otherwise unremarkable except for a history of dust allergies. Examination revealed normal vital signs, slight nasal congestion, and dry cough are noted during the examination. Cardiovascular, pulmonary, and abdominal examination findings are unremarkable (see reports). Chest radiograph: Normal. Spirometry: Slightly reduced FEV/FVC ratio of 70% which increased after bronchodilator challenge by 20%. Which of the following is the most appropriate diagnostic test to perform next?
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