Chart — Respiratory
Transudate vs Exudate Chart
The first fork after a thoracentesis: is the fluid a watery transudate (a pressure leak — think heart failure) or a protein-rich exudate (inflammation — think infection or cancer)? Light’s criteria decide.
Educational use only. Fluid interpretation is provider-directed and read in clinical context. This chart is an educational comparison aid. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Side by Side
| Feature | Transudate | Exudate |
|---|---|---|
| Mechanism | Pressure / oncotic imbalance ('leak') | Inflammation / increased capillary permeability |
| Protein content | LOW (watery) | HIGH (protein-rich) |
| Appearance | Clear, pale yellow | Cloudy, may be bloody or purulent |
| Light's criteria | Meets NONE | Meets ≥1: fluid/serum protein >0.5, fluid/serum LDH >0.6, or fluid LDH high |
| Typical causes | Heart failure, cirrhosis, nephrotic syndrome | Pneumonia/empyema, malignancy, PE, TB, pancreatitis |
Exam Traps
- ✦Transudate = watery, low-protein 'leak' from pressure (HF, cirrhosis, nephrotic).
- ✦Exudate = protein-rich, cloudy fluid from inflammation (infection, malignancy, PE, TB).
- ✦Light's criteria: an exudate meets ≥1 (high fluid/serum protein, high fluid/serum LDH, or high fluid LDH).
- ✦An infected, purulent exudate (empyema) needs drainage + antibiotics.
- ✦The fluid type narrows the cause — pair it with the clinical picture.
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with American Association for Respiratory Care (AARC) · GOLD (COPD) / ATS / CHEST. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →