Exploring Differential Diagnoses and Laboratory Studies for Poorly Controlled Asthma

JT is a 30 y/o male diagnosed with asthma three years ago. He tells you he is a city park maintenance worker, and the air quality in his city is poor. Despite regular use of inhaled corticosteroids (ICS), JTs disease is poorly controlled. Last year, he was in the ER with asthma exacerbations five times and was admitted twice. Oral glucocorticoids have helped him with his disease, but they have not been efficient. What specific questions will you ask JT to identify your differential diagnoses? What lab studies would you order, and how would you expect those results to vary?