Diagnosis of extrapulmonary tuberculosis by GeneXpert MTB/RIF Ultra assay.

INTRODUCTION: Diagnosis of extrapulmonary tuberculosis (EPTB) is an arduous task owing to different anatomical locations, unusual clinical presentations, and sparse bacillary load in clinical specimens. Although GeneXpert® MTB/RIF is a windfall in TB diagnostics including EPTB, it yields low sensitivities but high specificities in many EPTB specimens. To further improve the sensitivity of GeneXpert®, GeneXpert® Ultra, a fully nested real-time PCR targeting IS6110, IS1081 and rpoB (Rv0664) has been endorsed by the WHO (2017), wherein melt curve analysis is utilized to detect rifampicin-resistance (RIF-R). AREA COVERED: We described the assay chemistry/work design of Xpert Ultra and evaluated its performance in several EPTB types, that is, TB lymphadenitis, TB pleuritis, TB meningitis, and so on, against the microbiological reference standard or composite reference standard. Notably, Xpert Ultra exhibited better sensitivities than Xpert, but mostly at the compensation of specificity values. Moreover, Xpert Ultra exhibited low false-negative and false-positive RIF-R results, compared with Xpert. We also detailed other molecular tests, that is, Truenat MTBTM/TruPlus, commercial real-time PCR, line probe assay, and so on, for EPTB diagnosis. EXPERT OPINION: A combination of clinical features, imaging, histopathological findings, and Xpert Ultra are adequate for definite EPTB diagnosis so as to initiate an early anti-tubercular therapy.

We discussed the assay chemistry and evaluated performance of GeneXpert®MTB/RIF Ultra to identify the TB germs and resistance to one of the potent bactericidal drugs, that is, rifampicin in different types of extrapulmonary TB (EPTB, TB in organs other than lungs) and compared its performance with its ancestor, that is, GeneXpert. We briefly outlined the other molecular tests, such as Truenat MTB^TM/Truenat MTB^TM Plus, commercial real-time PCR, line probe assay, and so on for EPTB diagnosis. While evaluating Xpert Ultra results, the 'trace call' has been introduced, whose interpretation is important. By and large, Xpert Ultra assay outperformed in TB lymphadenitis, TB pleuritis, and TB meningitis when compared with Xpert, though limited information is available on other EPTB forms. Overall, the sensitivity of Xpert Ultra has been increased in most of EPTB cases, but mostly at the cost of specificity values.

Quantitative detection of mycobacterial mannophosphoinositides in tuberculosis patients by real-time immuno-PCR assay.

A real-time immuno-PCR assay was deliberated to detect mycobacterial mannophosphoinositides (PIMs). A dynamic range of PIMs (0.9 pg/mL-10 ng/mL) was detected in TB patients, wherein 88.2% and 81.1% sensitivities were obtained in pulmonary TB and extrapulmonary TB respectively, with 96-96.4% specificity. This assay may translate into a diagnostic kit.

Immuno-PCR, a new technique for the serodiagnosis of tuberculosis.

Rapid and accurate diagnosis of tuberculosis (TB) is essential to control the disease. The conventional microbiological tests have limitations and there is an urgent need to devise a simple, rapid and reliable point-of-care (POC) test. The failure of TB diagnostic tests based on antibody detection due to inconsistent and imprecise results has stimulated renewed interest in the development of rapid antigen detection methods. However, the World Health Organization (WHO) has emphasized to continue research for designing new antibody-based detection tests with improved accuracy. Immuno-polymerase chain reaction (I-PCR) combines the simplicity and versatility of enzyme-linked immunosorbent assay (ELISA) with the exponential amplification capacity and sensitivity of PCR thus leading to several-fold increase in sensitivity in comparison to analogous ELISA. In this review, we have described the serodiagnostic potential of I-PCR assays for an early diagnosis of TB based on the detection of potential mycobacterial antigens and circulating antibodies in body fluids of TB patients.

Diagnosis of tuberculosis based on the detection of a cocktail of mycobacterial antigen 85B, ESAT-6 and cord factor by immuno-PCR.

Attempts were made to enhance the sensitivity of immuno-PCR assay based on the detection of cocktail of mycobacterial antigen 85B (Rv1886c), ESAT-6 (Rv3875) and cord factor (trehalose 6,6'-dimycolate) in pulmonary and extrapulmonary TB patients. Detection of Ag85B was found to be superior to the detection of cocktail in TB patients.