Sensitivity of GeneXpert in pleural biopsy specimens in diagnosing tuberculosis in undiagnosed exudative pleural effusion

Pleural effusion is among the most common forms of paucibacillary extrapulmonary tuberculosis. Diagnosis is often clinical or based on elevated pleural fluid adenosine deaminase (ADA) levels. However, diagnostic uncertainty arises when clinical suspicion remains high despite low ADA levels, especially in patients already on empirical anti-tubercular therapy, which reduces bacillary load. The aim of this study is to evaluate the diagnostic utility of the Cartridge-Based Nucleic Acid Amplification Test (CBNAAT) in pleural biopsy samples with histopathologically confirmed tuberculosis. In this prospective study, 260 patients with undiagnosed pleural effusion who underwent pleural biopsy via thoracoscopy or ultrasound guidance were included. Histopathological examination identified 90 patients with pleural tuberculosis (study group) and 170 with non-tubercular etiology (control group). CBNAAT results from pleural biopsy specimens were analyzed to determine diagnostic performance. This study found the sensitivity, specificity, positive predictive value, and negative predictive value of CBNAAT for detecting pleural tuberculosis were 23.3% (21/90), 98.2% (167/170), 87.5% (21/24), and 70.8% (167/236), respectively. Sensitivity was higher (40%) in patients with pleural fluid ADA >40 IU/L compared to those with ADA <40 IU/L (15%). Notably, 4 of 90 patients (4.4%) in the study group were found to have rifampicin-resistant tuberculosis-these patients were on first-line anti-TB treatment at the time of biopsy. The conclusion of this study was that CBNAAT demonstrates low sensitivity but high specificity for diagnosing pleural tuberculosis from pleural biopsy samples. It is a valuable tool not only for early microbiological confirmation but also for detecting rifampicin resistance.