The effect of filtration on the cellular components in bronchoalveolar lavage fluid.

The effect of filtration through two layers of cotton gauze on the cellular composition of bronchoalveolar lavage (BAL) fluid was studied in 25 patients with pulmonary disease. There was no significant difference between median total cell count in unfiltered and filtered BAL (P = 0.73) or in the distribution of neutrophils or eosinophils. The percentage of bronchial epithelial cells was significantly higher in unfiltered than in filtered BAL (P = 0.02). Furthermore, differential cell counts showed a significantly lower percentage of alveolar macrophages (P = 0.04), and a significantly higher percentage of lymphocytes (P = 0.04) in unfiltered compared with filtered BAL. Thus, gauze filtration results in a loss of bronchial epithelial cells and lymphocytes, and is not recommended in the routine analysis of cellular components in BAL fluid.