Xpert MTB/RIF Ultra assay has higher sensitivity than the standard Xpert MTB/RIF for paucibacillary tuberculosis primarily because of:
- A Use of two separate molecular targets (rpoB and katG)
- B Incorporation of two additional IS6110 and IS1081 targets and a larger reaction volume ✓
- C Addition of a culture step before PCR amplification
- D Detection of lipoarabinomannan antigen alongside DNA
Correct answer: B. Incorporation of two additional IS6110 and IS1081 targets and a larger reaction volume
Explanation
Xpert MTB/RIF Ultra incorporates two IS6110 and IS1081 multicopy insertion sequences as additional PCR targets, combined with a larger reaction chamber (50 µL vs 15 µL), enabling detection of as few as 15.6 CFU/mL compared to ~131 CFU/mL for standard Xpert. This substantially improves sensitivity for smear-negative and extrapulmonary TB. The trade-off is slightly lower specificity due to detection of non-viable DNA, leading to 'trace' calls in treated patients. No culture step is involved — it remains a direct NAAT.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.