# Pleural Fluid Biomarkers in Focus: The Role of Cholesterol and Lactate Dehydrogenase (LDH) in Differentiating Exudative From Transudative Effusions

## TL;DR

This study shows that cholesterol levels in pleural fluid are more accurate than existing methods for identifying the type of pleural effusion.

## Contribution

The study demonstrates that pleural fluid cholesterol outperforms Light’s criteria in diagnosing exudative effusions.

## Key findings

- Pleural fluid cholesterol levels were significantly higher in exudative than transudative effusions.
- A cholesterol cutoff of 45 mg/dL achieved 98% sensitivity and 100% specificity for exudative effusions.
- Cholesterol outperformed traditional Light’s criteria parameters like protein and LDH ratios.

## Abstract

Background

Pleural effusion affects approximately 320 individuals per 100,000 population and can result from a wide range of pulmonary and extrapulmonary conditions. It may present as a complication of an existing illness or as an initial clinical sign, making accurate diagnosis and timely management essential. Under normal physiological conditions, the pleural space contains 7-16 mL of fluid (approximately 0.26 ± 0.1 mL/kg in healthy non-smokers). Effusion develops when fluid production exceeds clearance. Based on pathophysiology, pleural effusions are classified as either transudates or exudates. Light’s criteria remain the standard diagnostic tool but may misclassify up to 25% of cases. Recent studies suggest that pleural fluid cholesterol (pCHOL) may offer superior diagnostic accuracy.

Aim

This study aims to evaluate the reliability and diagnostic accuracy of pCHOL and lactate dehydrogenase (LDH) in distinguishing between transudative and exudative effusions in a tertiary care setting.

Methods

In this cross-sectional study, 80 patients with pleural effusion were classified as transudative (n = 30) or exudative (n = 50) based on clinical and radiological criteria. Paired pleural fluid and serum samples were collected. Pleural fluid protein, LDH, and cholesterol levels, as well as serum protein and LDH, were analyzed to apply Light’s criteria. Diagnostic performance was evaluated using sensitivity, specificity, and predictive values. Statistical analysis was conducted using IBM SPSS Statistics for Windows, Version 21.0 (Released 2012; IBM Corp., Armonk, NY, US), with p < 0.05 considered statistically significant.

Results

Mean pCHOL was significantly higher in exudative effusions (68.5 ± 20.3 mg/dL) than in transudative effusions (25.2 ± 9.6 mg/dL, p < 0.001). At a cutoff value of 45 mg/dL, pCHOL showed a sensitivity of 98% and specificity of 100%. This outperformed the pleural/serum protein ratio (78%/82%), pleural/serum LDH ratio (86%/93%), and pleural LDH level (88%/90%). The statistically significant difference in pCHOL levels underscores its superior diagnostic utility (p < 0.001).

Conclusion

pCHOL is a highly sensitive and specific biomarker for identifying exudative pleural effusions and demonstrates better diagnostic performance than Light’s criteria. Its simplicity, cost-effectiveness, and diagnostic reliability support its routine inclusion in pleural fluid analysis.