Background: Malignant pleural effusions are usually described as exudates. However, several studies have determined a high incidence of cytologically proved malignant effusions in transudates. The study aims to determine the compliance of cytologically proved malignant pleural effusions with Light's Criteria and to assess when it is necessary to perform more studies in transudates.
Methods: We have retrospectively reviewed all the cytologically positive effusions at our institution over six years. Biochemical characteristics were recorded, and Light's criteria were determined for each effusion. We analyzed the effusions' compliance with the criteria and determined whether its primary tumor or the presence of cirrhosis, acute kidney injury or congestive heart failure could interfere in the criteria being met.
Results: Overall, 224 patients presented malignant pleural effusions with biochemical pleural fluid analysis. Two (0.9%) were transudative effusions and two hundred and twenty-two (99.1%) were exudative effusions. Lung carcinoma, breast carcinoma and ovarian carcinoma were the most frequent primary tumors. One hundred and two (45.94%) patients met three Light criteria, 77 (34.68%) patients met two criteria and 43 (19.36%) met one criterion. Both patients with transudative malignant pleural effusions presented concomitant malignant ascites.
Conclusions: Malignant transudative pleural effusions were 0.9% of our patients. We found no relation between transudative malignant effusions and the presence of cirrhosis, acute kidney injury or congestive heart failure, or the type of tumor. We found no difference between the tumor type and the distribution of Light's criteria met.