In a patient with pleural effusion, which pleural fluid finding is most characteristic of a chylothorax?

Question

Accepted Answer

A. Pleural fluid triglyceride level > 110 mg/dL with positive Sudan Black stain. ## Chylothorax: Diagnostic Criteria

**Key Point:** Chylothorax is diagnosed by **elevated pleural fluid triglycerides (>110 mg/dL)** combined with **positive Sudan Black or Oil Red O stain**, which identifies chylomicrons.

### Diagnostic Thresholds for Chylothorax

| Finding | Diagnostic Significance |
|---------|------------------------|
| **Triglycerides > 110 mg/dL** | Highly specific (>99%) for chylothorax |
| **Triglycerides 50–110 mg/dL** | Requires lipoprotein electrophoresis to confirm |
| **Triglycerides < 50 mg/dL** | Chylothorax unlikely |
| **Sudan Black or Oil Red O stain** | Identifies chylomicrons (lipoproteins) |
| **Appearance** | Milky/opalescent (but not always visible) |

**High-Yield:** The **triglyceride level** is the single most useful test. A level >110 mg/dL is virtually diagnostic without need for further testing. Levels 50–110 mg/dL require lipoprotein electrophoresis.

**Clinical Pearl:** Chylothorax is most commonly caused by **lymphatic obstruction** (malignancy, tuberculosis, post-thoracic surgery) or **lymphatic disruption** (trauma). In children, congenital lymphangiectasia is a common cause.

**Mnemonic:** **TLC** = Triglycerides > 110, Lipoproteins (chylomicrons), Chylothorax confirmed.

Answer

B. Pleural fluid LDH > 1000 IU/L with hemorrhagic appearance

Answer

C. Pleural fluid cholesterol > 200 mg/dL with needle-shaped crystals

Answer

D. Pleural fluid glucose < 30 mg/dL with low pH

In a patient with pleural effusion, which pleural fluid finding is most characteristic of a chylothorax?

Explanation

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