This is a prospective study of benign and malignant pleural effusions carried out to determine the diagnostic yield of standard cytopathology compared to findings of DNA ploidy obtained by flow cytometry. Twenty-six samples of pleural effusion obtained by thoracocentesis were analyzed by cytopathology and flow cytometry. Final diagnosis was confirmed in all instances by histopathology of pleural biopsies. Ten samples were excluded from the analysis due to technical reasons, and the remaining 16 were used in the study. There were 13 malignant and 3 benign pleural effusions. Cytopathology revealed 9 malignant effusions and 7 benign effusions (4 false negatives). Flow cytometry findings have shown euploid DNA content in all 3 benign effusions (positive predictive value and specificity of 100%) and in 8 malignant effusions (positive value and specificity of 100%) and in 8 malignant effusions (sensitivity of 38.4% and negative predictive value of 27.2%). Cytopathology showed specificity of 100%, sensitivity of 69.2%, and positive and negative predictive values of 100% and 42.8%, respectively. The authors concluded that in this study the low sensitivity and negative value of flow cytometry in comparison to conventional cytopathology have limited the usefulness of flow cytometry to the finding of euploid DNA contents in benign pleural effusions.

Keywords: Flow cytometry. Cytopathology. DNA ploidy. Pleural effusion.