What are normal pleural cholesterol levels?

Normal Pleural Cholesterol Levels

Normal pleural fluid cholesterol levels are typically less than 45-60 mg/dL, with values above this threshold indicating exudative effusions rather than transudates. 1

Diagnostic Thresholds

Standard Cutoff Values

• Pleural fluid cholesterol <45-60 mg/dL indicates a transudate 2, 3, 4, 5
• Pleural fluid cholesterol ≥60 mg/dL indicates an exudate 1, 2
• Some studies support a lower cutoff of 45-50 mg/dL with excellent diagnostic performance 3, 4

Diagnostic Performance

• At a cutoff of 60 mg/dL, pleural cholesterol demonstrates 95-100% sensitivity and 80-100% specificity for identifying exudates 6, 2
• At a cutoff of 45 mg/dL, sensitivity reaches 98% with 100% specificity 4
• This outperforms Light's criteria, which misclassifies 10-25% of cases 4, 5

Clinical Context by Effusion Type

Transudative Effusions

• Mean cholesterol levels: 25-30 mg/dL 2, 4
• Typically associated with heart failure, cirrhosis, nephrotic syndrome 6, 2

Exudative Effusions

• Malignant effusions: mean cholesterol 90-94 mg/dL 2, 4
• Inflammatory effusions: mean cholesterol 68-76 mg/dL 2, 4
• Pseudochylothorax: cholesterol >200 mg/dL (5.18 mmol/L) with cholesterol crystals present 1

Special Diagnostic Considerations

Pseudochylothorax vs. Chylothorax

• Pseudochylothorax is defined by pleural cholesterol >200 mg/dL (>5.18 mmol/L) with absence of chylomicrons and presence of cholesterol crystals 1
• Results from long-standing effusions with markedly thickened, fibrotic pleura 1
• Most commonly caused by chronic rheumatoid pleurisy, tuberculosis, or poorly treated empyema 1

Practical Advantages Over Light's Criteria

• Requires only pleural fluid sample—no simultaneous serum sample needed 6
• More cost-effective with only two laboratory determinations 6
• Superior specificity (85.71%) compared to Light's criteria (71.43%) 5
• Elevated cholesterol in exudates appears independent of serum cholesterol levels 2

Common Pitfalls

• Do not rely solely on pleural/serum cholesterol ratio (PC/SC ≥0.4), as it shows lower sensitivity (81%) and specificity (57%) compared to absolute cholesterol values 3
• Light's criteria may misclassify up to 25% of transudates as exudates, particularly in patients on diuretics 4, 5
• Cholesterol measurement should be combined with clinical context and imaging findings for optimal diagnostic accuracy 6, 5