Introduction: Although pleural effusion is a common clinical manifestation, the differential diagnosis of the cause of pleural effusion is often challenging, especially in the early differentiation of tuberculous pleurisy (TP) from other pleural effusion. The aim of this study was to evaluate the performance of commonly used laboratory tests for the early diagnosis of difficult cases of pleural effusion. Methods: Patients with undiagnosed pleural effusion were enrolled and subjected to five laboratory tests including thoracoscopy, pleural fluid adenosine deaminase assay (ADA), serum tuberculosis antibody test (TB-antibody), tuberculin skin test (TST), and T-SPOT.TB assay. The diagnosis of TP was established based on pleural histology and mycobacterial culture. The different tests were compared for diagnostic performance. Results: A total of 106 patients were enrolled; their mean age was 53 years and 70.8% were male. Seventy-two (68%) of them were confirmed to have TP. When used individually, the five laboratory tests showed highly variable performance parameters, including sensitivity ranging from 46% to 92% and specificity ranging from 33% to 82%. When used in different combinations, thoracoscopy combined with TST or TB-antibody showed the optimal performance parameters, with a sensitivity of 80.8% and a specificity of 85.7%. Conclusions: The results of this study suggest that the combination of thoracoscopy with TST or TB-antibody test is the best choice for the early diagnosis of difficult cases of TP in high TB burden countries. Keywords: Tuberculous pleural effusion, Early diagnosis, Thoracoscopy, Adenosine deaminase, Tuberculin skin test, Tuberculosis antibody test, T-SPOT.TB assay
