A proof of concept study on the diagnostic utility of in vivo expressed mycobacterial transcripts in tuberculous pleuritis

Tuberculous pleuritis (TBP) is the second most common extra-pulmonary manifestation of tuberculosis. Histopathology using pleural biopsy is the most sensitive diagnostic procedure for TBP. Since biopsy acquisition is invasive, better biomarkers for diagnosis using pleural fluid are needed. The current study was designed to identify mycobacterial RNA biomarkers in TBP and to assess their diagnostic utility in pleural fluid. 261 TBP suspects were recruited for the study. 45 suspects were excluded and remaining (n = 216) were divided into TBP (n = 54) and non-TBP (n = 162) groups based on composite reference standard (CRS). Whole genome microarray was carried using M.tb RNA from pleural biopsies of TBP patients. The data was validated using qRT-PCR and the diagnostic utility of top two highly expressed genes was evaluated in pleural fluid, using qualitative real time RT-PCR. 1856 genes were differentially expressed in microarray with 1365 upregulated and 491 downregulated genes. The diagnostic utility of transcripts corresponding to two genes, Rv1586c and Rv2819c was assessed post microarray validation. The presence of either of two genes led to pleural TB identification with 79.6% sensitivity and 93.28% specificity. Thus, the transcripts of genes Rv1586c and Rv2819c holds potential for development of RNA based diagnostic assay for TBP using pleural fluid.