In acute eosinophilic pneumonia (AEP), Pulmonary function tests show reduced forced vital capacity and total lung capacity with a normal forced expiratory volume in one second; diffusing capacity for carbon monoxide (DLCO) is commonly reduced. Bronchoalveolar lavage (BAL) is performed in the majority of patients to exclude infection, hemorrhage, or malignancy. The BAL is performed using a sequential instillation and recovery of 50 to 60 mL. The median BAL cellularity was 350,000/mm3. BAL eosinophilia was present in all cases with a median of 38%. Lung biopsy is rarely necessary to make a diagnosis of AEP in immunocompetent patients with a compatible history and prominent BAL eosinophilia in the absence of infection or other known precipitant.

Pulmonary function tests^[1]

• A restrictive process may be noted: Reduced forced vital capacity and total lung capacity with a normal forced expiratory volume in one second; diffusing capacity for carbon monoxide (DLCO) is commonly reduced.^[2]

Bronchoscopy with bronchoalveolar lavage

• Bronchoalveolar lavage (BAL) is performed in the majority of patients to exclude infection, hemorrhage, or malignancy.^[3]
• The BAL is performed using a sequential instillation and recovery of 50 to 60 mL aliquots in an area of radiographic opacity.
• In acute pneumonia, the BAL fluid typically shows a very high proportion (>25 percent) and total number of eosinophils.^[4]
• The median BAL cellularity was 350,000/mm3. BAL eosinophilia was present in all cases with a median of 38%.
• The proportion of BAL lymphocytes is approximately 10 to 30 percent and the proportion of BAL neutrophils is 1 to 16 percent.
• The level of eosinophilia returns to normal when the illness resolves.

Lung biopsy

• Lung biopsy is rarely necessary to make a diagnosis of AEP in immunocompetent patients with a compatible history and prominent BAL eosinophilia in the absence of infection or another known precipitant.
• Indications for lung biopsy would include concern about an infectious etiology that could not be quickly excluded by BAL or failure to respond to systemic glucocorticoids.