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BAL Fluid

Patients with AEP may be clinically indistinguishable from those with ARDS or an infectious process, and BAL fluid provides an important clue to the diagnosis of AEP. Although similar in clinical presentation, BAL fluid eosinophilic percentages and total numbers are markedly increased in AEP, ARDS is usually associated with increased neutrophils, and most viral and bacterial pneumonias typically are not characterized by BAL eosinophilia. Correlation between BAL eosinophilia and eosinophilic pneumonia in biopsy specimens has been demonstrated in several studies. As a result, it has been suggested that in the appropriate clinical setting, BAL eosinophilia is itself adequate justification for a trial of corticosteroids without tissue biopsy. When BAL eosinophilia is present, the patient should be evaluated for known causes of pulmonary eosinophilia. BAL fluid should be cultured and stained for infectious agents, as the most important point in the differential diagnosis is the exclusion of an infectious process.