Pleural Effusion

Classifying Pleural Effusions

  • A pleural effusion is an accumulation of fluid within the pleural space
  • Determining the underlying cause is facilitated by thoracentesis and pleural fluid analysis
  • The pleural fluid may be classified as a transudate or an exudate, depending on the etiology
  • Transudates occur secondary to conditions which cause an increase in the pulmonary capillary hydrostatic pressure or a decrease in the capillary oncotic pressure
  • Leads to accumulation of protein poor pleural fluid
  • Common causes include: CHF, nephrotic syndrome, cirrhosis, hypoalbuminemia, pulmonary embolism
  • Exudates occur secondary to conditions which cause inflammation or increased pleural vascular permeability
  • Leads to accumulation of protein rich pleural fluid and cells
  • Common causes include: pneumonia, cancer, tuberculosis, pulmonary embolism
  • According to Light’s criteria, if at least one of the following criteria is present, then the fluid is determined to be an exudate:
  • Pleural fluid protein to serum protein ratio greater than 0.5
  • Pleural fluid LDH to serum LDH ratio greater than 0.6
  • Pleural fluid LDH greater than two-thirds the upper limit for normal serum LDH


  • Often asymptomatic, but can present with dyspnea, pleuritic chest pain, and cough
  • Physical examination may demonstrate decreased breath sounds on the side of the effusion, dullness to percussion, and decreased tactile fremitus


  • Chest x-ray: blunting of costophrenic angles; free-flowing effusions will result in layering of fluid on the decubitus view
  • Chest CT sometimes used for further evaluation


  • Treat underlying cause
  • Thoracentesis is diagnostic and therapeutic
  • Pleurodesis or indwelling catheter for recurrent/malignant effusions