Discriminative performance of serum, pleural fluid, and gradient high-sensitivity C-reactive protein in pleural effusions

Background Pleural effusion is a common clinical condition with diverse etiologies. Differentiating exudative from transudative pleural effusions is essential for appropriate diagnosis and management. High-sensitivity C-reactive protein (hs-CRP) has been investigated as a potential biomarker in the evaluation of pleural effusion. This study aimed to assess the discriminative performance of pleural fluid hs-CRP, serum hs-CRP, the serum–pleural fluid hs-CRP gradient, and the pleural fluid/serum hs-CRP ratio in differentiating exudative from transudative pleural effusions classified according to Light’s criteria. Methods This cross-sectional study included 62 patients with pleural effusion. Levels of hs-CRP, total protein, and lactate dehydrogenase were measured in pleural fluid and serum. Differences between groups were analyzed using the Mann–Whitney U test. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis, and multivariable logistic regression was performed to assess the independent association of hs-CRP parameters with exudative pleural effusion after adjustment for potential confounding variables. Results The mean age of participants was 52.3 ± 16.0 years, and 53.2% were male. Exudative effusion accounted for 58.1% of cases, with parapneumonic effusion representing the most common etiology (33.9%). Pleural fluid hs-CRP, serum hs-CRP, and the serum–pleural fluid hs-CRP gradient were significantly higher in exudative effusions (all P < 0.001). The area under the curve values for pleural fluid hs-CRP, serum hs-CRP, and the hs-CRP gradient were 0.866 (95% CI: 0.775–0.958), 0.845 (95% CI: 0.746–0.943), and 0.762 (95% CI: 0.641–0.883), respectively. Pleural fluid hs-CRP showed the best discriminative performance and, at a cutoff value of 2.20 mg/dL, achieved a sensitivity of 63.9% and a specificity of 100%. Multivariable logistic regression showed that pleural fluid hs-CRP, serum hs-CRP, and the serum–pleural fluid hs-CRP gradient remained significantly associated with exudative pleural effusion after adjustment for potential confounding variables. Conclusions Pleural fluid hs-CRP, serum hs-CRP, and the serum–pleural fluid hs-CRP gradient demonstrated good discriminative performance for differentiating exudative from transudative pleural effusions according to Light’s criteria. Among these parameters, pleural fluid hs-CRP demonstrated the highest discriminative performance with the highest specificity and diagnostic accuracy. The pleural fluid/serum hs-CRP ratio did not provide additional discriminatory value.