Which test rapidly detects rifampin resistance as a proxy for MDR-TB?

• A. Chest X-ray
• B. GeneXpert MTB/RIF
• C. MGIT culture
• D. Sputum smear

Answer: (B)

Rapid detection of rifampin resistance to act as a surrogate for MDR-TB. The GeneXpert MTB/RIF test is a molecular assay that quickly detects Mycobacterium tuberculosis and, by identifying mutations in the rpoB gene, determines rifampin resistance within about two hours. Because rifampin resistance strongly correlates with MDR-TB, this result guides urgent treatment and infection-control decisions far faster than culture-based drug susceptibility testing, which can take weeks. Other options do not provide drug-resistance information: chest X-ray shows imaging findings, not resistance; MGIT culture withDrug susceptibility testing is accurate but slow; sputum smear only shows bacteria, not susceptibility.