Light's criteria: pleural exudate
Classifies a pleural effusion as exudate or transudate by the three biochemical criteria.
When to use
Pleural effusion of undetermined cause where exudate and transudate must be separated.
Pearls and pitfalls
- Any one of the three criteria is enough to classify the fluid as an exudate.
- Sensitivity for an exudate is close to 100% and specificity is around 70%, so the criteria alone can call a transudate an exudate.
- The pleural LDH criterion uses two thirds of the laboratory serum LDH upper limit.
- The criteria do not identify the cause of the effusion, only the type of fluid.
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Formula
Exudate if pleural LDH is above two thirds of the serum upper limit, or pleural to serum LDH is above 0.6, or pleural to serum protein is above 0.5.
Evidence
Classic biochemical criteria separating exudate from transudate, with accuracy described in pleural effusion cohorts.
References
- Yang DN, Xu YN, Niu Y, et al. Effects of Light's criteria on the diagnostic accuracy of pleural fluid carcinoembryonic antigen concentrations for malignant pleural effusion. Sci Rep. 2025;15:17726. doi:10.1038/s41598-025-17726-3
Frequently asked questions
What is Light's criteria: pleural exudate?
Classifies a pleural effusion as exudate or transudate by the three biochemical criteria. Pleural effusion of undetermined cause where exudate and transudate must be separated.
How is the result calculated?
Exudate if pleural LDH is above two thirds of the serum upper limit, or pleural to serum LDH is above 0.6, or pleural to serum protein is above 0.5.
How should the result be interpreted?
Classic biochemical criteria separating exudate from transudate, with accuracy described in pleural effusion cohorts.
What are the sources?
Yang DN, Xu YN, Niu Y, et al. Effects of Light's criteria on the diagnostic accuracy of pleural fluid carcinoembryonic antigen concentrations for malignant pleural effusion. Sci Rep. 2025;15:17726.