Baseline demographics are shown in Table 1. Compared with IPF, patients with persistent HP were younger, more likely to be female, less likely to be ever smokers, had fewer pack-years of smoking, and had less crackles on auscultatory lung examination. Patients with HP had greater physiologic obstruction (based on FEV1 and FEV1/FVC), whereas patients with IPF had greater restriction and lower diffusing capacity. Patients with HP had a lower radiographic fibrosis score (median score, 11.04 for HP vs 15.00 for IPF). Patients with HP with and without biopsy specimens did not differ with respect to clinical characteristics, symptoms, physiologic function, antigen exposure, number of lung transplants, or number of deaths (e-Table 1). Sixty-five patients with HP had an identifiable antigen exposure (75% were avian, and 25% were microbial) (e-Table 1). These patients were instructed to perform specific abatement procedures (eg, removal of bird, extensive cleaning of home environment, removal of down products, remediation of sources of water-damaged structures, and changing residence if possible). Of these 65 patients, 25% underwent home industrial-hygienist evaluations. Treatment modalities at initial clinic visit included current use of prednisone in 45.2% of patients (80 of 177) and/or other immunomodulation therapy (ie, mycophenolate mofetil, azathioprine, and/or cyclophosphamide) in 7.9% of patients (14 of 177) and are summarized in e-Table 2.