Clinical suspicion with falling hematocrit
Radiographic imaging consistent with bilateral infiltration (CXR, CT) - can be patchy, focal or<unk> 
Bronchoscopy with BAL showing sequentially increasing RBC counts
Diffuse alveolar hemorrhage
Idiopathic small vessel vasculitis
Immersion pulmonary edema
Granulomatosis with polyangiitis 
Flash pulmonary edema
Churg-Strauss syndrome
Reexpansion pulmonary edema
Microscopic polyangitis