Introduction: The aims of this study were to determine the distribution of transudates and exudates among pathologically proven malignant pleural effusions, and to demonstrate the necessity for cytologic studies in patients with a transudative effusion.Materials and Methods: This study is a retrospective review of all subjects diagnosed with malignant or paramalignant pleural effusion over a 10-year period at a tertiary hospital. The study included 67 subjects with malignant mesothelioma, 45 subjects with metastatic disease, and 36 subjects with paramalignant effusions. Results: There were 55 female and 93 male subjects; the mean age of the sample was 62 years. Malignant pleural effusions were transudative in 1.5% of malignant mesotheliomas, 6.8% of metastatic diseases, and 11.1% of paramalignant effusions. Conclusions: Cytological examination of pleural fluid in patients with unexplained transudative effusion is essential to rule out malignant processes.
According to Light’s criteria, an exudate is defined by at least one of the following: a total protein pleural fluid to serum ratio greater than 0.5, an lactate dehydrogenase (LDH) pleural fluid to serum ratio greater than 0.6, or an absolute pleural fluid LDH greater than 2/3 of the upper normal limit of the normal serum LDH value. A transudate is any pleural effusion that does not meet the aforementioned criteria.
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