Background: Conventional biomarkers cannot always establish the cause of pleural effusions, so alternative tests permitting rapid and accurate diagnosis are required. The primary aim of this study was to assess the ability of pentraxin-3 and calprotectin to diagnose pleural effusions and compare their efficacy to that of other conventional markers. Methods: We studied 128 patients with pleural effusions, classified as transudates and exudates including malignant, tuberculous, and parapneumonic effusions (MPE, TPE and PPE) and empyema. The pleural fluid levels of pentraxin-3 (PTX3), calprotectin, C-reactive protein (CRP), soluble triggering receptor expressed on myeloid cells-1 (sTREM-1), procalcitonin (PCT) and lactate were assessed. Results: Calprotectin, CRP, PCT, and lactate levels were significantly higher in patients with exudates than transudates. PTX3 yielded the most favorable sensitivity and specificity to discriminate PPE from MPE or TPE, providing an AUC=0.74 (95%CI 0.63-0.84), a sensitivity=62.07%, and a specificity=81.08%, with a cut-off point of 25.00 ng/ml. Conclusion: Our data suggest that calprotectin was limited in its ability to differentiate between exudative pleural effusions of different origins. However, PTX3 may allow improved differentiation of PPE from MPE or TPE compared to the previously identified biomarkers CRP, sTREM-1, and PCT.