Quantitative C-reactive protein for differentiating tuberculous and malignant pleural effusion: A cross-sectional study.

Purpose: Pulmonary or pleural tuberculosis and malignancy are the most common causes of lymphocyte-rich pleural effusion. In resource-limited settings, establishing a definitive diagnosis for patients with pleural effusion (PEs) may be challenging, emphasizing the need for a simple diagnostic test. This study aimed to investigate the diagnostic value of quantitative C-reactive protein (qCRP) for differentiating between tuberculous pleural effusion (TPE) and malignant pleural effusion (MPE).

Methods: A cross-sectional study was performed on 81 patients admitted for lymphocyte-rich exudative pleural effusion at a tertiary care center. Comprehensive biochemical analyses, including qCRP levels in the pleural fluid and pathological examinations of blood, pleural fluid, and/or tissue, were performed. The t-test was used for continuous variables, and the chi-square test was used for categorical variables. To assess the independent associations between variables, multivariate logistic regression analysis was performed. The diagnostic performance of pleural fluid qCRP levels was evaluated using a receiver operating characteristic (ROC) curve.

Results: Forty-four (54.3%) patients were diagnosed with TPE and 34 (42.0%) with MPE. The qCRP levels in the pleural fluid were significantly greater in the TPE group than in the MPE group (55.5 ± 45.9 mg/L vs. 18.6 ± 19.1 mg/L, P < 0.001). The cutoff value for pleural fluid CRP levels (≥ 24.1 mg/L) yielded a sensitivity of 65.9% and a specificity of 73.5% in predicting TPE.

Conclusions: Pleural fluid qCRP is a simple, rapid, cost-effective diagnostic tool for differentiating tuberculous from malignant etiology in patients with lymphocyte-rich exudative pleural effusion.

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Supplementary information: The online version contains supplementary material available at 10.1007/s12055-025-01978-9.