Which rapid molecular test can detect rifampin resistance quickly in suspected MDR-TB?

• A. Sputum culture
• B. Line Probe Assay
• C. GeneXpert MTB/RIF
• D. Chest X-ray

Answer: (C)

Understanding rapid detection of rifampin resistance hinges on tests that look for genetic changes in the TB bacteria. The GeneXpert MTB/RIF assay is an automated, cartridge-based real-time PCR test that detects Mycobacterium tuberculosis and rifampin resistance by identifying mutations in the rpoB gene. It delivers results in about two hours from sputum, making it a quick and practical way to flag suspected MDR-TB and start appropriate treatment early. Sputum culture, while the definitive method for TB and drug susceptibility, takes weeks to yield results, so it isn’t rapid. Line Probe Assay can also detect rifampin resistance directly from specimens or cultures, but it requires more specialized lab setup and has a longer turnaround than GeneXpert. Chest X-ray, meanwhile, is an imaging test and cannot determine rifampin resistance.