Characteristic changes in the proportions of leukocyte populations in bronchoalveolar lavage (BAL) reflect different disease states in the lung. The standard method for examination of BAL leukocytes is by microscopy of cytospin preparations. This method may not be the optimum technique due to difficulties in distinguishing cell types morphologically and due to the low number of cells routinely counted. We hypothesized that flow cytometry (FCM) may be a more precise tool for investigating BAL.
100 BALs were performed on 92 patients. All samples were stained using the pan-leukocyte marker (CD45) in combination with a granulocyte marker (CD15) and a cell viability marker (7-aminoactinomycin D). Selected samples were also stained with an eosinophil marker (CD23). These samples were run on an FCM and the results compared with leukocyte differentials obtained by light microscopy of parallel cytospin preparations.
Close correlations between the two methods were demonstrated for the enumeration of all leukocyte subsets, but the coefficient of variation was considerably lower by FCM than by cytospin.
These findings, combined with the speed of FCM and the ability to perform simple lymphocyte phenotyping, argue in favor of this becoming the method of choice for investigating BAL.