BackgroundThe presence of tumour cells in pleural fluid or tissue defines an effusion as malignant. Cytology

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62(5):585-90. PURPOSE:To evaluate the clinical and laboratory characteristics of pleural effusions secondary to tuberculosis (TB) or cancer (CA). METHODS: A total of 326 patients with pleural effusion due to TB (n=182) or CA (n=144) were studied. The following parameters were analyzed: patient gender, age and pleural effusion characteristics (size, location, macroscopic fluid aspect, protein concentration, lactate dehydrogenase (DHL) and adenosine deaminase activity (ADA) and nucleated cell counts). RESULTS: Young male patients predominated in the tuberculosis group. The effusions were generally moderate in size and unilateral in both groups. Yellow-citrine fluid with higher protein (p < 0.001) levels predominated in effusions from the tuberculosis group (5.3 + 0.8 g/dL) when compared to the CA group (4.2 ± 1.0 g/dL), whereas DHL levels were more elevated in CA (1,177 ± 675 x 1,030 ± 788 IU; p = 0.003) than in TB. As expected, ADA activity was higher in the TB group (107.6 ± 44.2 x 30.6 ± 57.5 U/L; p < 0.001). Both types of effusions presented with high nucleated cell counts, which were more pronounced in the malignant group (p < 0.001). TB effusion was characterized by a larger percentage of leukocytes and lymphocytes (p < 0.001) and a smaller number of mesothelial cells (p = 0.005). Lymphocytes and macrophages were the predominant nucleated cell in neoplastic effusions. CONCLUSION: Our results demonstrate that in lymphocytic pleural exudate obtained from patients with clinical and radiological evidence of tuberculosis, protein and ADA were the parameters that better characterize these effusions. In the same way, when the clinical suspicion is malignancy, serous-hemorrhagic lymphocytic fluid should be submitted to oncotic cytology once this easy and inexpensive exam reaches a high diagnostic performance (≅ 80%). In this context, we suggest thoracocentesis with fluid biochemical and cytological examination as the first diagnostic approach for these patients.

The proposed models were effective in suggesting pleural tuberculosis or cancer.

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This study confirms that storage time and temperature are potential pre-analytical causes of error in pleural fluid cytology.

Pleural fluid samples collected in EDTA and sent for analysis within 1 h after collection can be used to determine ADA up to 28 days after collection if stored at 4 degrees C or -20 degrees C, with no evidence of significant increases or decrease in enzyme activity that might distort the results.

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