Background: The profile of leukocytes in bronchoalveolar lavage (BAL) fluid provides important information for diagnosing various lung diseases. A differential cell count of BAL is conventionally performed by evaluating centrifuged samples under a light microscope and enumerating the stained cells. Another rarely used method to identify BAL leukocytes is flow cytometry (FCM). However, there are no guidelines for standardizing this method and related literature is limited. This study aimed to evaluate the accuracy of FCM for identifying BAL leukocytes.
Methods: The BAL samples accepted to the hematology laboratory between 2014 - 2018 were retrospectively evaluated via light microscopy (LM) by a hematologist; while flow cytometric analyses with a monoclonal antibody panel composed of CD45/CD14/CD16 were noted by another doctor. The percentages of macrophages, lymphocytes, neutrophils and eosinophils determined by both methods were recorded for analysis. Correlations between the results from LM and FCM were investigated. In addition, compatibility between LM and FCM for denoting pathological values for each cell type was checked.
Results: Among 140 reviewed BAL samples, 76 were included for further analysis. Comparisons revealed strong correlations between FCM and LM for identifying macrophages, lymphocytes, neutrophils, and eosinophils. In addition, regarding the normal cutoff values for each leukocyte type, FCM and LM were similar in the identification of pathological changes of all cell types except eosinophils.
Conclusions: Flow cytometry was found to be feasible for use instead of LM and might become a more widely used technique to analyze BAL fluid in the future.