What is the Difference Between Exudative and Transudative Pleural Effusion?

The difference between exudative and transudative pleural effusion lies in their causes and the biochemical characteristics of the fluid. Pleural effusions are categorized as either transudates or exudates based on these characteristics.

Transudative Pleural Effusion:

• Caused by an imbalance in hydrostatic and oncotic forces, usually resulting from increased hydrostatic pressure or decreased plasma oncotic pressure.
• Common causes include heart failure, nephrotic syndrome, cirrhosis, and hypoalbuminemia.
• The fluid is typically protein-poor.
• Transudative effusions usually respond to treatment of the underlying condition, such as diuretic therapy.

Exudative Pleural Effusion:

• Result from increased capillary permeability, leading to the leakage of protein, cells, and other serum constituents.
• Common causes include pneumonia, cancer, tuberculosis, and pulmonary embolism.
• The fluid is typically protein-rich and may contain cells.
• Requires further investigation to determine the cause and appropriate treatment.

According to Light's criteria, a pleural effusion is classified as an exudate if at least one of the following criteria is present:

1. Pleural fluid protein to serum protein ratio greater than 0.5
2. Pleural fluid LDH to serum LDH ratio greater than 0.6
3. Pleural fluid LDH greater than two-thirds the upper limit for normal serum LDH

Determining whether a pleural effusion is transudative or exudative helps in identifying the underlying cause and guiding appropriate treatment.

Comparative Table: Exudative vs Transudative Pleural Effusion

The main difference between exudative and transudative pleural effusions lies in their causes and biochemical characteristics. Here is a table summarizing the differences between the two types:

Transudative effusions are caused by conditions that alter pleural permeability and oncotic pressure, such as congestive heart failure, liver cirrhosis, and nephrotic syndrome. On the other hand, exudative effusions are caused by inflammation or increased pleural vascular permeability, as seen in malignancy, infection, trauma, pulmonary infarction, and pulmonary embolism.