The Xpert MTB/RIF Ultra assay differs from the first-generation Xpert MTB/RIF in which important diagnostic feature?
- A It uses a different DNA target region and detects both rpoB and katG mutations
- B It requires 8 hours to produce results versus 2 hours
- C It has improved sensitivity for paucibacillary disease due to two additional insertion-sequence targets (IS6110 and IS1081) alongside rpoB detection ✓
- D It detects resistance to isoniazid and pyrazinamide in addition to rifampicin
Explanation
Xpert MTB/RIF Ultra includes two additional highly repetitive targets — IS6110 (present in up to 16 copies) and IS1081 (present in 6 copies per M. tuberculosis genome) — in addition to the rpoB RRDR region, significantly boosting sensitivity for paucibacillary TB such as smear-negative pulmonary TB and extrapulmonary TB. Ultra has approximately 5% improved sensitivity over standard Xpert at the cost of marginally lower specificity (more 'trace' calls). Both assays produce results within 2 hours. Detection remains limited to rifampicin resistance (rpoB); katG and pyrazinamide resistance are not targets.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.