Role of biochemical tests in the diagnosis of exudative pleural effusions

To examine the diagnostic utility of pleural adenosine deaminase (PADA), pleural lactate dehydrogenase (PLDH), and several other biochemical tests in bronchogenic carcinoma and malignant mesothelioma, and to compare biochemical characteristics of their fluid with nonmalignant pleural effusions.

This study consisted of 226 patients diagnosed with malignant (75), tuberculous (65), and parapneumonic pleural effusions (86). We examined the following biochemical parameters in the pleural fluid and serum: adenosine deaminase, lactate dehydrogenase, glucose level, protein level, pleural fluid/serum ADA ratio (P/S ADA), P/S LDH ratio, and P/S protein ratio.

Parapneumonic pleural effusions had a significantly higher level of PLDH and of P/S LDH than malignant and tuberculous pleural effusions (P = 0.000), and malignant pleural effusions had a higher level of PLDH than tuberculous pleural effusions. Tuberculous and parapneumonic effusions had significantly higher levels of PADA than those of malignant effusions (P = 0.000). When the 54 patients having bronchogenic carcinoma were compared to the remaining 21 mesothelioma patients, the former had a lower median level of PADA (P = 0.001) with a higher level of PLDH (P = 0.05).

Our results show that high pleural LDH and low PADA levels are suggestive of pleural effusion due to bronchogenic carcinoma, whereas high levels of PADA alone can be indicative of tuberculous pleural effusion and high levels of both markers can show complicated parapneumonic effusions or empyema.