Calculators · Respiratory Medicine · Criteria

Light's criteria for pleural effusion

Also called Lights criteria, exudate vs transudate, pleural fluid analysis

Separates exudative from transudative pleural effusions using protein and LDH.

U/L
U/L
U/L

Fill 5 more fields to see the result.

Formula and scoring

Exudate if any: pleural/serum protein >0.5; pleural/serum LDH >0.6; pleural LDH >⅔ of the upper limit of normal serum LDH.

Exam and ward pearls

  • Light's criteria are close to 100% sensitive for exudates but up to one-third of transudates are misclassified as exudates, particularly in patients on diuretics.

When not to rely on it

  • Interpret a borderline exudate in a patient on diuretics with clinical context.

Source

  1. Light RW, Macgregor MI, Luchsinger PC, Ball WC Jr. Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med. 1972;77(4):507-13. doi:10.7326/0003-4819-77-4-507 · PMID 4642731
  2. Subedi et al. Comparative evaluation of pleural fluid cholesterol and total protein versus Light's criteria in differentiation of exudates and transudates. Clin Respir J. 2025;19(9):e70121. (States the three criteria.) doi:10.1111/crj.70121 · PMID 40867084

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

More Respiratory Medicine calculators