Diagnostic significance of increased bronchoalveolar lavage fluid eosinophils

We determined the incidence of increased bronchoalveolar lavage (BAL) fluid eosinophil percentages in 1,059 consecutive patients undergoing bronchoscopy with BAL over a 33-month period. Forty-eight (48) patients were found to have 5% or more BAL eosinophils. The most common causes for increased BAL eosinophils were interstitial lung diseases (40% of patients), acquired immunodeficiency syndrome (AIDS)-associated pneumonia (17% of patients), idiopathic eosinophilic pneumonia (15% of patients), and drug-induced lung disease (12% of patients). Together, these four diagnoses accounted for 84% of all patients. In contrast, eosinophils were uncommon in the BAL of patients with the adult respiratory distress syndrome, lung cancer, community-acquired pneumonia, or immunocompromising diseases other than AIDS. The finding of increased BAL eosinophils was most helpful in patients presenting with unexplained pulmonary infiltrates. In these patients, this finding was often an important clue to the final diagnosis. We conclude that although the finding of an increased percentage of BAL eosinophils is uncommon, when present it is relatively specific for a limited number of diseases.