Interpretation
| Result | Meaning |
|---|---|
| 0 criteria | Transudate (e.g. heart failure, cirrhosis, nephrotic syndrome) |
| ≥1 criterion | Exudate (e.g. parapneumonic, malignancy, TB, PE) |
Formula
Exudate if any: pleural protein ÷ serum protein >0.5 · pleural LDH ÷ serum LDH >0.6 · pleural LDH >⅔ × upper limit of normal serum LDH
Clinical pearls
- About 25% of transudates in patients on diuretics (e.g. heart failure) are misclassified as exudates; if clinically a transudate, check serum–pleural albumin gradient >1.2 g/dL or protein gradient >3.1 g/dL.
- Sensitivity for exudate is ~98% but specificity is lower; the criteria favour calling an exudate.
Examples
light's criteria pleural protein 4.0 serum protein 6.0 pleural ldh 300 serum ldh 200 uln 220exudate or transudate: fluid protein 2 g/dL, serum protein 7, fluid LDH 100, serum LDH 250, LDH upper limit 220
FAQ
What are Light's criteria?
An effusion is an exudate if pleural/serum protein >0.5, pleural/serum LDH >0.6, or pleural LDH >2/3 of the serum LDH upper limit of normal.
What if a heart failure patient on diuretics meets exudate criteria?
Check the serum-to-pleural albumin gradient; >1.2 g/dL suggests the effusion is actually a transudate.