Light's Criteria: Exudative Effusions will have at least one of the following:

• Pleural fluid protein / Serum protein > 0.5
• Pleural fluid LDH / Serum LDH > 0.6
• Pleural fluid LDH > 2/3 * Serum LDH Upper Limit of Normal

Note: While Light's Criteria are reported to be highly sensitive for exudative effusions, their specificity for exudative effusions is only 83%.

Light RW. Clinical practice. Pleural effusion. N Engl J Med. 2002 Jun 20;346(25):1971-7. PubMed PMID: 12075059.