🫁 Light's Criteria (Pleural Effusion)
Classify a pleural effusion as exudate or transudate with Light's criteria.
Clinical takeaway
Any one positive criterion = exudate.
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When to use
Direct the work-up of a pleural effusion.
How it works
Exudate if any: pleural/serum protein > 0.5, pleural/serum LDH > 0.6, or pleural LDH > ⅔ of the serum LDH upper limit of normal.
Key points
- Any one positive criterion = exudate.
- Very sensitive; can misclassify diuresed transudates.
- Use the albumin gradient if results are discordant with the clinical picture.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Pleural fluid protein | 4 g/dL |
|---|---|
| Serum protein | 7 g/dL |
| Pleural fluid LDH | 300 U/L |
| Serum LDH | 200 U/L |
| Serum LDH upper limit of normal | 240 U/L |
→Effusion typeExudate
- Protein ratio > 0.5：0.57 ✓
- LDH ratio > 0.6：1.50 ✓
- Pleural LDH > ⅔ ULN：300 vs 160 ✓
Frequently asked questions
- What is Light's Criteria (Pleural Effusion)?
- Classify a pleural effusion as exudate or transudate with Light's criteria.
- How is Light's Criteria (Pleural Effusion) calculated? What is the core formula?
- Exudate if any: pleural/serum protein > 0.5, pleural/serum LDH > 0.6, or pleural LDH > ⅔ of the serum LDH upper limit of normal.
- When is Light's Criteria (Pleural Effusion) used?
- Direct the work-up of a pleural effusion.
- What are the key clinical points for Light's Criteria (Pleural Effusion)?
- Any one positive criterion = exudate. Very sensitive; can misclassify diuresed transudates. Use the albumin gradient if results are discordant with the clinical picture.
- What are the limits and cautions when using Light's Criteria (Pleural Effusion)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Light's Criteria (Pleural Effusion) calculated in practice? Can you show a worked example?
- Inputs: Pleural fluid protein 4 g/dL, Serum protein 7 g/dL, Pleural fluid LDH 300 U/L, Serum LDH 200 U/L, Serum LDH upper limit of normal 240 U/L → Result: Effusion type Exudate（Protein ratio > 0.5: 0.57 ✓, LDH ratio > 0.6: 1.50 ✓, Pleural LDH > ⅔ ULN: 300 vs 160 ✓）