What are examples of conditions that cause exudative and transudative pleural effusions?

Examples of Transudative and Exudative Pleural Effusions

Transudative effusions result from altered hydrostatic forces with normal capillary permeability, while exudative effusions arise from pleural surface inflammation or increased capillary permeability—each category has distinct common causes that guide clinical management. 1

Transudative Pleural Effusions

Most Common Causes

• Heart failure is the leading cause, accounting for more than 80% of all transudates and representing 29% of all pleural effusions 2, 3
• Liver cirrhosis accounts for approximately 10% of transudates, typically occurring in patients who also have ascites 2, 3
• Hypoalbuminemia from any cause (including nephrotic syndrome) creates low oncotic pressure leading to fluid accumulation 2, 4

Additional Transudate Causes

• End-stage renal failure causes effusions in 24.7% of patients through multiple mechanisms including fluid overload, hypoalbuminemia, and salt retention 2, 4
• Dialysis-related fluid imbalances 1
• Atelectasis 2

Key Clinical Point

Clinical assessment alone can correctly identify transudative effusions in appropriate settings (such as left ventricular failure with confirmatory chest radiograph), and these do not require sampling unless atypical features are present or they fail to respond to treatment. 1

Exudative Pleural Effusions

Most Common Causes

• Malignancy accounts for 26-42% of all pleural effusions and is the leading exudative cause 2, 3

  • Lung cancer is the most common malignant cause (25-52% of malignant effusions) 2, 4
  • Breast cancer is the second most common (3-27% of malignant effusions) 2, 4
  • Lymphomas (Hodgkin's and non-Hodgkin's) account for approximately 10% of malignant effusions 2, 5

• Pneumonia and parapneumonic effusions represent 16% of all pleural effusions, with approximately 40% of pneumonia patients developing effusions 2, 3

• Tuberculosis accounts for 6% of all pleural effusions and is the most common infectious cause of exudative lymphocytic effusions 2, 5

• Pulmonary embolism causes small effusions in up to 40% of cases, with 80% being bloodstained 2, 3

Additional Exudate Causes

• Post-surgical effusions (4% of all effusions) 2
• Rheumatoid arthritis occurs in 5% of RA patients 2
• Systemic lupus erythematosus affects up to 50% of SLE patients during disease course 2, 5
• Drug-induced effusions from medications including methotrexate, procarbazine, cyclophosphamide, bleomycin, anthracyclines, and tyrosine kinase inhibitors (now the most common drug cause) 1, 4
• Multiple myeloma causes effusions in approximately 6% of cases with characteristically high pleural protein values 5
• Empyema (10.56% of exudative effusions) 6

Special Population Considerations

• HIV patients: Leading causes are Kaposi's sarcoma, parapneumonic effusions, and tuberculosis 2
• Cancer patients on chemotherapy: Anthracyclines cause cardiotoxicity leading to cardiogenic effusions, while dasatinib causes pulmonary hypertension in 5% of patients 4

Critical Diagnostic Distinctions

Pathophysiologic Mechanisms

• Transudates: Altered hydrostatic/oncotic pressure balance with intact pleural membranes and normal capillary permeability 1, 4
• Exudates: Pleural surface inflammation, increased capillary permeability, or disrupted lymphatic drainage 1, 4

Common Pitfalls to Avoid

• Light's criteria misclassification: 25-30% of cardiac and liver transudates are incorrectly classified as exudates when using Light's criteria alone 2, 5
• Pulmonary embolism: Approximately 75% of PE patients with effusion have pleuritic pain, but pleural fluid tests are unhelpful for diagnosis—maintain high clinical suspicion 1
• Bilateral effusions: Do not exclude malignancy based on bilaterality alone 4
• Drug history: Always obtain detailed medication history as drug-induced effusions are often overlooked 1
• Asbestos exposure: Always obtain occupational history when investigating pleural effusions to identify potential mesothelioma 5