Respiratory Diseases

Exudative and Transudative Pleural Effusion



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A pleural effusion is defined as an abnormal accumulation of fluid in the pleural space (the space just outside the lung and just inside the ribcage). Different types of fluid may gather in the pleural space and may be due to several different causes. The types of pleural effusions can be grouped in to two large categories, transudative and exudative.


Exudative effusion:

The exudative form of pleural effusion is the result of inflammation which causes leaky capillaries. The exudative fluid that leaks from the capillaries is rich in protein.


Exudative pleural effusions most commonly occur in individuals with pneumonia. If the fluid itself becomes infected the pleural effusion may then be called an "empyema". If the fluid is there long enough for fibrous formation to occur in the pleural space, then the fluid may become a "loculated effusion" (locked in place).


Common causes of exudative pleural effusions include:

1. Bacterial infection

2. Viral infection

3. Tuberculosis infection

4. Neoplasm (cancer)

5. Pulmonary embolism with infarct

6. Collagen vascular disease

7. Pancreatitis

8. Hemothorax

9. Sarcoidosis

10. Uremia

11. Asbestos exposure

12. Pericardial disease

13. Chylothorax


Transudative effusion:

The transudative form of pleural effusion occurs in indviduals with intact capillaries. Protein can't leak through so the pleural fluid is protein-poor and is described as an ultrafiltrate of plasma (the fluid your blood cells are in inside of your vessels). Transudative fluid is due to increased hydrostatic pressure and/or decreased oncotic pressure inside the blood vessels.


Common causes of transudative pleural effusions include:

1. Congestive heart failure "CHF"

2. Cirrhosis

3. Nephrotic syndrome

4. Peritoneal dialysis

5. Superior vena cava obstruction

6. Myxedema

7. Urinothorax

8. Protein-losing enteropathy

9. Pulmonary embolism


An individual with a pleural effusion may complain of difficulty breathing or chest pain when breathing in or out, but often this individual is asymptomatic. The effusion is usually detected on chest x-ray.


An upright chest x-ray may show blunting of the costophrenic angles. This means there is fluid in the edges where the diaphragm meets the ribs below the lungs. If a chest x-ray is obtained with the patient lying down it may be possible to determine whether the pleural fluid is free flowing or loculated.


The definitive diagnostic test for a pleural effusion is called thoracentesis. When a thoracentesis is performed, a large needle is used to remove some of the pleural fluid. The pleural fluid can then be sent to the lab to identify whether it is transudative (protein-poor) or exudative (protein-rich).


Often the fluid will also be tested in other ways. For example, the presence of bacteria is determined with a gram stain and culture. Glucose, pH, amylase and a CBC with differential will also be determined on the pleural fluid. Each of these tests gives further clues to diagnosis and optimal treatment of a transudative or exudative pleural effusion.


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