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Test Findings

Positive Light's Criteria



  • Light's criteria are used to determine the nature of a pleural fluid sample, and narrow down the differential diagnosis of a pleural effusion. 
  • A pleural fluid sample is most likely exudate if one or more of the criteria are met.
    • Criteria

    • Pleural fluid : serum protein ratio >0.5
    • Pleural fluid : serum LDH ratio >0.6
    • Pleural fluid LDH > ⅔ of upper limit of normal serum LDH
    • Causes of Positive Light's Criteria

    • Malignancy
    • Infection - parapneumonic effusion, empyema, viral, fungal, TB, ruptured abscess / cyst
    • Pulmonary embolism (90% exudative)
    • Autoimmune disease - rheumatoid pleuritis, SLE
    • Pancreatitis
    • Haemothorax
    • Chylothorax
    • Asbestosis
    • Uraemia
    • Oesophageal rupture
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