Performing thoracentesis is used to remove excess pleural fluid. The fluid is then analyzed to determine if its transudative or exudative. Transudates are substances that have passed through a membrane and usually occur in low protein states. Exudates are substances that have escaped from blood vessels. They contain an accumulation of cells and have a high specific gravity and a high lactate dehydrogenase level. Exudates usually occur in response to a malignancy. infection. or inflammatory process. A chest tube is rarely necessary because the amount of fluid typically isnt large enough to warrant such a measure. Pleural effusions cant drain by themselves.