Light's Criteria
Exudate if any of three rules: protein ratio >0.5, LDH ratio >0.6, or pleural LDH >⅔ serum LDH ULN.
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How it works
Light’s criteria help separate exudative from transudative effusions using simultaneous serum and pleural chemistries.
Limits
CHF “pseudoexudates,” paraproteinemia, and laboratory variability exist; Light’s is one piece of pleural evaluation alongside cell count, Gram stain/culture, cytology, and imaging.
Educational tool only—not for diagnosis or treatment decisions.