Pleural effusions and thoracentesis
Pleural effusion, either unilateral or bilateral, may be caused by many different diseases of the lung, pleura or other organs, or by systemic diseases. Characterization of pleural fluid either as exudate or transsudate helps in diagnostic workout. Exudate is usually caused by a disease of the lung or pleura or by a systemic disease. Transsudate is usually caused by heart failure or by a hepatic or renal disease.