Background: Pleural tuberculosis (pTB) is a diagnostic challenge because of its non-specific clinical features, lack of accurate diagnostic tools and paucibacillary nature of the disease. Methods: We, here describe the development of a novel magnetic nanoparticle antibody-conjugate and aptamer-based assay (MNp-Ab-Ap assay) targeting 4 different Mycobacterium tuberculosis (M. tb.) antigens (GlcB, MPT51, MPT64 and CFP-10) for pTB diagnosis. The MNp-Ab-Ap assay was developed by conjugating polyclonal antibodies on the surface of magnetic nanoparticles (MNPs) by using EDC-NHS chemistry. These conjugated MNPs were used to capture M. tb. antigens present in the pleural fluid samples. The resulting antigen-antibody complex was detected by antigen-specific 5'-biotinylated aptamers. All assays were standardized using samples of the 'Development set' (n=17) and evaluated in the 'Validation set' (n=114) in a blinded manner. Patient categorization was done using a 'Composite Reference Standard'. Assay cut-offs were determined from the 'Development set' (n=17; 'Definite & Probable' pTB; n=9 and 'Non-TB'; n=8) by calculating mean+3SD of OD450 values of the 'Non-TB' group and applied to 'Validation set' (n=114; 'Definite' pTB; n=8, 'Probable' pTB; n=34, 'Possible' pTB; n=28 and 'Non-TB'; n=44). Results: Out of the 4 assays, MPT51-based MNp-Ab-Ap assay performed the best with 66.6% (95%CI;50.4-80.4) sensitivity and 95.4% (95%CI;85.1-99.4) specificity in the combined 'Definite and Probable' pTB group. Xpert MTB/RIF assay detected only six samples in the 'Validation set'. Binary logistic regression analysis indicated that MPT51-based MNp-Ab-Ap assay provided an incremental advantage over the existing diagnostic algorithm for pTB. Conclusions: We conclude that MPT51-based MNp-Ab-Ap assay is a novel technique that can pave the way towards rapid and accurate diagnosis of pTB.
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