Pleural Effusion Diagnosis and Classification

Introduction to Pleural Effusion

The British Thoracic Society and European Respiratory Society guidelines establish Light's criteria as the gold standard for distinguishing transudates from exudates [1][2]

A pleural effusion is classified as an exudate if one or more of the following are met: pleural fluid LDH >2/3 the upper limit of normal serum LDH [1][2]

Heart failure is the most common cause of transudative effusions, accounting for 29-53.5% of all pleural effusions and the majority of bilateral effusions 2
Liver cirrhosis causes transudates in approximately 3-10% of cases 2
Tuberculosis always causes exudative effusions with high LDH and protein ratios, typically with lymphocyte predominance 2
The European Respiratory Society notes that 25-30% of cardiac and hepatic transudates are misclassified as exudates by Light's criteria 2

Serum-effusion albumin gradient >1.2 g/dL reclassifies the effusion as a transudate due to heart failure 2
NT-proBNP levels >1500 μg/mL in serum or pleural fluid accurately diagnose heart failure 2