Diagnostic thoracentesis in which cells are extracted from the pleural cavity is commonly done when the possibility of mesothelioma exists however in up to of cases the fluid tests negative or inconclusive even though cancer is present. Less common symptoms of pleural mesothelioma include fever night sweats and weight loss. Information on the symptoms diagnosis staging and treatment of peritoneal mesothelioma. Any excess fluid is absorbed by blood and lymph vessels maintaining a balance. To determine whether a fluid is a transudate or exudate a diagnostic thoracentesis in which a needle or catheter is used to obtain a fluid sample may be conducted. The most common cause of transudative fluid is congestive heart failure.