Effect of filtration and concentration on the composition of bronchoalveolar lavage fluid

The effects of filtration and concentration on the cellular and protein composition of bronchoalveolar lavage fluids were examined in ten normal subjects and 11 patients with asthma. Filtration of lavage fluid preferentially removed bronchial epithelial cells, resulting in a relative increase in the proportion of alveolar macrophages. Concentration of the lavage fluid results in a significant loss of proteins, with a greater loss of large molecular weight proteins. A similar loss was not observed when diluted sera form the same subjects were concentrated in the same manner. Our results suggest that when studying the cellular composition of bronchoalveolar lavage fluid, the aspirated fluid should not be filtered through cotton gauze if changes in the bronchial epithelium may be of importance because it will remove a significant proportion of these cells. Proteins in lavage fluids should be quantitated in unconcentrated lavage fluid whenever possible.