Which rapid diagnostic test detects rifampin resistance and is widely used in TB clinics?

• A. Chest x-ray
• B. Culture on Löwenstein-Jensen
• C. Tuberculin skin test
• D. GeneXpert MTB/RIF assay

Answer: (D)

The test that detects rifampin resistance and is widely used in TB clinics is a cartridge-based molecular assay that quickly looks for Mycobacterium tuberculosis and mutations in the rifampin resistance–determining region of the rpoB gene. It provides results in about two hours, allowing clinicians to diagnose TB and identify rifampin resistance promptly, which is crucial because rifampin resistance strongly suggests MDR-TB and guides immediate, effective treatment choices. This rapid insight helps start appropriate regimens sooner and limit transmission.

Chest X-ray might suggest TB but cannot confirm rifampin resistance. Culture on Löwenstein-Jensen is the traditional gold standard for TB culture and drug susceptibility testing but is slow, taking weeks, so it isn’t a rapid diagnostic. Tuberculin skin testing detects exposure or infection status and does not inform about active TB or drug resistance.