Utility of flow cytometry analysis for pleural and peritoneal fluids

Introduction Pleural and peritoneal/ascites fluid samples with many lymphocytes are commonly received in the cytology laboratory. It is often difficult to distinguish reactive lymphocytes from hematopoietic malignancy based on morphology alone, however. Flow cytometry can be a useful adjunct in body fluids, although literature on this subject is limited. Materials and methods This study is a single-institution 5-year retrospective review of 377 fluid samples from 341 patients with corresponding flow cytometry analysis. The cytologic findings were correlated with the flow cytometry results and clinical data, as available. Results Of 4158 pleural fluids received over 5 years, 325 (7.8%) had corresponding flow cytometry analysis. Of these 325 samples, 57 (17.5%) were positive for hematopoietic malignancy by flow cytometry. Of the positive cases, only 24 (8.7%) represented a new diagnosis of hematopoietic malignancy (ie, did not have a known history). Of 3020 peritoneal/ascites fluids received over 5 years, 52 (2%) had corresponding flow cytometry. Of these, 8 were positive for hematopoietic malignancy, and only 2 represented a presumed new diagnosis. Conclusions Routine flow cytometry analysis for pleural and peritoneal/ascitic fluids is of limited utility, with only rare cases positive for hematopoietic malignancy without a known history. Of these cases, many had atypical cells that suggested a positive diagnosis. Conversely, in cases with a known history, about 75% were positive for hematopoietic malignancy. Our study suggests that the utility of flow cytometry for pleural and peritoneal/ascitic fluids is limited, and should be used sparingly in cases without atypical cytologic features, high clinical suspicion, or known history.