What criteria do you use to decide when to perform a BAL in hypersensitivity pneumonitis? Do you perform it on every suspected case, or are there specific indications you look for before proceeding with BAL?  

Short answer: When the vibes are right.I know that's a flippant answer, but that's an honest-to-God real answer.Long answer: This is really complicated and personally, I'm frustrated by our guidelines and the level of evidence we have for diagnosing HP. To answer the question, it's worth delineating...