Light's Criteria 

Updated: Apr 13, 2017
  • Author: James J Lamberg, DO; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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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

See the list below:

  • 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

See the list below:

  • 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


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

See the list below:

  • 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