ABSTRACT
Pleural fluid accumulation occurs as a consequence of several physiological factors that influence pleural fluid formation or absorption. Pleural effusions develop whenever the rate of pleural fluid accumulation in the pleural space exceeds the rate of reabsorption. Pleural effusions are generally classified as exudative or transudative (1). The following criteria are used to characterize transudative pleural effusions:
1. The ratio of the pleural fluid to the serum protein level is less than 0.5. 2. The ratio of the pleural fluid to the serum LDH level is less than 0.6. 3. The absolute level of the pleural fluid LDH level is less than 200 IU/L.
