A 49-year-old woman is evaluated for a 4-month history of dry cough and paroxysmal coughing spells that make conversation difficult. She has a history of dust allergies and was unsuccessfully treated for allergic rhinitis. Physical examination and chest radiograph are normal. Spirometry shows a slightly reduced FEV1/FVC ratio of 70% which increased by 20% after bronchodilator challenge. Which of the following is the most appropriate diagnostic test to perform next?
September 4, 2026 86
