Diagnostic yield of thoracoscopic pleural biopsy in undiagnosed exudative pleural effusion and comparative analysis of pleural fluid adenosine deaminase levels

Undiagnosed exudative pleural effusion remains a frequent clinical challenge, particularly in high-burden settings where tuberculosis and malignancy predominate. Pleural fluid adenosine deaminase (ADA) is useful for suggesting tuberculous pleural effusion (TPE), but a substantial "gray zone" overlaps with malignant pleural effusion (MPE). This study evaluated the diagnostic yield of medical thoracoscopy with comparative analysis of pleural fluid ADA levels. This prospective, single-center, exploratory observational study was conducted over 1.5 years in a tertiary care hospital of north India. Consecutive adults (>18 years) with undiagnosed exudative pleural effusion (Light's criteria) were enrolled after pleural fluid CBNAAT/GeneXpert was negative for Mycobacterium tuberculosis and pleural fluid cytology negative for malignancy on at least two samples, taken ≥24 hours apart. A total of 150 patients were included (92 males, 58 females). All patients underwent single-port medical thoracoscopy under conscious sedation, systematic pleural inspection, and targeted biopsy (3-6 samples). Biopsies were sent for histopathology and CBNAAT. Thoracoscopic pleural biopsy established malignancy in 104/150 (69.3%) and tuberculosis in 40/150 (26.7%) patients, resulting in an overall diagnostic yield of 96%. Non-specific inflammation was observed in four patients, pyogenic inflammation in one, and one biopsy was inconclusive. Metastatic adenocarcinoma was the commonest malignancy (88/104). In biopsy-proven TPE, tissue CBNAAT positivity was low (9/40, 22.5%). ADA was significantly higher in tubercular effusions than MPE (40.17 vs. 20.11 IU/L; p<0.001). Major complications were infrequent with no procedure-related mortality.