LIGHT'S CRITERIA
Determination of transudate versus exudate source of pleural effusion
Fluid is exudate if one of the following Light’s criteria is present:[1, 2, 3, 4]
- Effusion protein/serum protein ratio greater than 0.5
- Effusion lactate dehydrogenase (LDH)/serum LDH ratio greater than 0.6
- Effusion LDH level greater than two-thirds the upper limit of the laboratory's reference range of serum LDH
Exudative effusions
- Abdominal fluid: Abscess in tissues near lung, ascites, Meigs syndrome, pancreatitis
- Connective-tissue disease: Churg-Strauss disease, lupus, rheumatoid arthritis, Wegener granulomatosis
- Endocrine: Hypothyroidism, ovarian hyperstimulation
- Iatrogenic: Drug-induced, esophageal perforation, feeding tube in lung
- Infectious: Abscess in tissues near lung, bacterial pneumonia, fungal disease, parasites, tuberculosis
- Inflammatory: Acute respiratory distress syndrome (ARDS), asbestosis, pancreatitis, radiation, sarcoidosis, uremia
- Lymphatic abnormalities: Chylothorax, malignancy, lymphangiectasia
- Malignancy: Carcinoma, lymphoma, leukemia, mesothelioma, paraproteinemia
Transudative effusions
- Atelectasis: Due to increased negative intrapleural pressure
- Cerebrospinal fluid (CSF) leak into pleural space: Thoracic spine injury, ventriculoperitoneal (VP) shunt dysfunction
- Heart failure
- Hepatic hydrothorax
- Hypoalbuminemia
- Iatrogenic: Misplaced catheter into lung
- Nephrotic syndrome
- Peritoneal dialysis
- Urinothorax: Due to obstructive uropathy
Exceptions
These are processes that typically cause exudative effusions, but may cause transudative effusions.
- Amyloidosis
- Chylothorax
- Constrictive pericarditis
- Hypothyroid pleural effusion
- Malignancy
- Pulmonary embolism
- Sarcoidosis
- Superior vena cava obstruction
- Trapped lung
Leading causes of pleural effusion
- Congestive heart failure (transudate), incidence 500,000/year
- Pneumonia (exudate), incidence 300,000/year
- Cancer (exudate), incidence 200,000/year
- Pulmonary embolus (transudate or exudate), incidence 150,000/year
- Viral disease (exudate), incidence 100,000/year
- Coronary-artery bypass surgery (exudate), incidence 60,000/year
- Cirrhosis with ascites (transudate), incidence 50,000/year
Test sensitivity and specificity for exudate
Table 1. Test Sensitivity and Specificity for Exudate (Open Table in a new window)
| Sensitivity, % | Specificity, % | |
| Light’s criteria | 98 | 83 |
| Protein/serum protein ratio >0.5 | 85 | 84 |
| LDH/serum LDH ratio >0.6 | 90 | 82 |
| LDH >2/3 upper limits of serum normal | 82 | 89 |
| Pleural-fluid cholesterol level >60 mg/dL | 54 | 92 |
| Pleural-fluid cholesterol level >43 mg/dL | 75 | 80 |
| Pleural-fluid/serum cholesterol ratio >0.3 | 89 | 81 |
| Serum/pleural-fluid albumin level ≤1.2 g/dL | 87 | 92 |
