Comparison of the different methods for counting cell in the bronchoalveolar lavage fluid

Objectives: Differential cell pattern of bronchoalveolar lavage (BAL) fluid is used in the diagnostic approach of diffuse paranchymal lung diseases and in narrowing the differential diagnoses. The purpose of this study is to obtain the cellular profile of the BAL fluid by flow cytometry which is faster and more objective compared to optical microscopy and to determine the suitability or advantage of using flow microscopy instead of optical microscopy. Materials and Methods: The study was performed by retrospectively reviewing on patients who underwent bronchoalveolar lavage for diagnostic purpose due to diffuse parenchymal lung disease between 2017 and 2018, and whose BAL fluids were analyzed both in optical microscopy and in flow cytometry device. Findings: Wilcoxon signed rank test showed significant differences between FCM and optical microscopy in terms of the number of lymphocyte and eosinophil (p=0.005, p=<0,001 respectively). However, the difference between FCM and optical microscopy interms of both the number of alveolar macrophages and the number of neutrophils is not significant (p=0.820, p=<0,280 respectively). With Bland-Altman analysis, we found that flow cytometry predicts the number of lymphocyte by 34.4% and the number of neutrophil by 14% lower, when compared to optical microscopy. However, the distribution of alveolar macrophage populations was homogeneous. Multivariate point and line diagrams show that there is no significant difference between flow cytometry and optical microscopy for eosinophils when eosinophils are considered. Results: Our study indicates that in the case of appropriate clinical conditions and accessibility, FCM which provides faster results and better reflect the alveolar cell population can be used safely in differential cell profile analysis of BAL fluid. Keywords: Bronchoalveolar lavage, differential cell count, optical microscopy, flow cytometry