Diagnostic Utility of RT-PCR in Extra-Pulmonary (Pleural and Peritoneal) Tuberculosis

Background: Conventional diagnostic tests for pleural and peritoneal TB include microscopy, culture and histopathological examination. These have recognised limitations for clinical use due to the paucity of acid-fast Bacilli in these specimens and the invasive nature of sample collection for histopathological examination. We carried our study to evaluate the efficacy of REAL-TIME PCR (RT-PCR) for the diagnosis of TB in pleural effusion and Ascites. We also compared the efficiency of RTPCR with a conventional technique for the diagnosis of Peritoneal and Pleural TB. In addition, the efficacy of RT-PCR with conventional PCR was also studied.

Methods: A total of 90 patients with pleural effusion and/or ascites having clinically suspected TB were studied. They were divided into two groups. Group 1 or cases included diagnosed Tubercular Pleural/ Ascitic Fluid (Pleural Fluid ADA > 70 IU/L/ Ascitic Fluid ADA >30 IU/L/ Fluid AFB stain and Histology i.e., Granulomas from biopsy/ Bronchoscopy / Laparoscopy). Group 2 or controls included non-Tubercular lymphocytic exudative Pleural/Ascitic fluids. RT PCR MTB-SYBR GREEN AND PCR were carried in all study participants while RT-PCR by TAQMAN was done in 25 randomly selected participants (19 from group 1/ cases and 6 from group2/controls).

Results: We found that for tubercular pleural effusion, RT-PCR MTB-SYBR GREEN had a sensitivity of 51.2% and a specificity of 100 percent whereas for tubercular ascites it was 50 percent and 100 percent, respectively. The combined sensitivity and specificity for RTPCR-SYBR GREEN in our study (Pleural TB + peritoneal TB) was 50.9 % and 100 % respectively. The sensitivity and specificity calculated for RT PCR TAQMAN PROBE in diagnosing extrapulmonary TB was 68.4% and 100% respectively.

Conclusion: RT-PCR for extrapulmonary TB (pleural and peritoneal) had better specificity when compared to conventional methods, and also better sensitivity than most of the conventional methods except for ADA and Mantoux, which had low specificity as compared to RT-PCR. RT-PCR by Taqman technique showed better sensitivity and specificity when compared to conventional techniques including conventional PCR and RT-PCR by Sybr Green assay. A decision to treat pleural & peritoneal TB should not depend entirely on RT-PCR result.