Leaky fluid: This is caused by excessive production of normal pleural fluid and is commonly associated with congestive heart failure and hypoproteinemia. Leaky fluid is clear in appearance, transparent or pale yellow in colour, low in pleural fluid protein and does not clot when left to stand.
Exudate: It is caused by damage to the pleura due to inflammation, etc., and exudes excessive fluid. It is commonly seen in diseases such as septic and bacterial infections and malignant tumour pleural metastases. The exudate is cloudy in appearance and contains red blood cells, white blood cells, bacteria, tumour cells, etc. The pleural fluid is high in protein and tends to clot when left to stand.