What is the cause of pleuristic fluid?

Pleural fluid: Pleural fluid rests in the pleural space outside the lung but inside the chest wall. It can be increased due to infection, inflammation, heart failure, cancer, and other causes.

Pleural fluid: Can result from pleuritis (or pleurisy), pneumonia, pulmonary embolus/infarction, congestive heart failure, cancer, injury (sometimes iatrogenic), intra abdominal abscess. As you can see, nothing good. Have your doctor take a careful look at it..