The Xpert MTB/RIF Ultra assay (GeneXpert Ultra) is performed on a sputum specimen from a suspected pulmonary TB patient with HIV. The result shows 'MTB detected TRACE; RIF resistance NOT detected'. What is the correct interpretation?
- A Trace result indicates very low bacillary load; clinical and radiological correlation needed; repeat testing recommended before starting treatment in non-endemic settings ✓
- B Confirmed TB — trace results always indicate active TB and treatment should start
- C RIF sensitive confirmed — start standard HRZE for 6 months
- D The result is invalid; another assay (LAMP) must be used
Explanation
GeneXpert Ultra introduced a new 'Trace' category (below the semi-quantitative levels of Very Low, Low, Medium, High) to improve sensitivity, especially in paucibacillary and HIV-associated TB. WHO guidance specifies that a Trace result requires careful clinical and radiological correlation: in high-burden settings or immunocompromised individuals, it should generally prompt treatment; in low-burden settings it may represent non-viable or environmental NTM DNA and repeat testing is recommended. The Trace category improves sensitivity for smear-negative TB but reduces specificity compared to standard Xpert MTB/RIF.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.