Investigation and management

The British Thoracic Society (BTS) produced guidelines in 2010 covering the investigation of patients with a pleural effusion.

Imaging

• posterioranterior (PA) chest x-rays should be performed in all patients
• ultrasound is recommended: it increases the likelihood of successful pleural aspiration and is sensitive for detecting pleural fluid septations
• contrast CT is now increasingly performed to investigate the underlying cause, particularly for exudative effusions

Massive left pleural effusion in a patient with a history of cancer. Note the mediastinal shift to the right. - e Image used on license from Radiopaedia

Pleural aspiration

• as above, ultrasound is recommended to reduce the complication rate
• a 21G needle and 50ml syringe should be used
• fluid should be sent for pH, protein, lactate dehydrogenase (LDH), cytology and microbiology

Light's criteria

was developed in 1972 to help distinguish between a transudate and an exudate. The BTS recommend using the criteria for borderline cases:

• exudates have a protein level of >30 g/L, transudates have a protein level of <30 g/L
• if the protein level is between 25-35 g/L, Light's criteria should be applied. An exudate is likely if at least one of the following criteria are met:
  • pleural fluid protein divided by serum protein >0.5
  • pleural fluid LDH divided by serum LDH >0.6
  • pleural fluid LDH more than two-thirds the upper limits of normal serum LDH

Other characteristic pleural fluid findings:

• low glucose: rheumatoid arthritis, tuberculosis
• raised amylase: pancreatitis, oesophageal perforation
• low complement (C3, C4): systemic lupus erythematosus (SLE)
  • pleural effusions occur in approximately 30-50% of SLE patients during the course of their disease and may be the presenting feature
• heavy blood staining: mesothelioma, pulmonary embolism, tuberculosis