Diagnostic accuracy of Xpert MTB/RIF Ultra for abdominal tuberculosis in a tertiary care setting in North India

Background Abdominal tuberculosis (TB) poses diagnostic difficulties due to its vague symptoms and low bacterial load. Culture, the gold standard, is limited by a prolonged turnaround time of up to eight weeks. Xpert MTB/RIF Ultra (Xpert Ultra), a rapid, automated molecular test, can detect Mycobacterium tuberculosis and rifampicin resistance in under two hours. This study evaluated the diagnostic accuracy of Xpert Ultra for abdominal TB using both culture and a composite reference standard (CRS), and assessed its agreement in rifampicin resistance detection with phenotypic and genotypic drug susceptibility testing (DST). Methods A prospective observational study was conducted from September 2019 to March 2021 at a tertiary care centre in North India. Adults with clinical and radiological features of abdominal TB were enrolled. Relevant abdominal samples were collected and tested using smear, culture (BACTEC MGIT 960), Xpert Ultra, histopathology, and clinical response. Rifampicin resistance was confirmed using MGIT 960 and GenoType MTBDRplus. Results Of 176 eligible patients, 144 were enrolled, yielding 152 abdominal samples: lymph node aspirates (52%), biopsies (42.8%), pus/aspirates (3.3%), and ascitic/omental fluids (2%). Xpert Ultra showed 84% diagnostic accuracy against CRS and 75% against culture. Rifampicin resistance detection showed 100% concordance with both phenotypic and genotypic DST. Conclusion Xpert Ultra offers high diagnostic accuracy and excellent concordance in rifampicin resistance detection for abdominal TB. Its speed and reliability make it a valuable diagnostic tool in high-burden settings.