Which test rapidly detects TB and rifampin resistance from a sputum sample?

• A. Ziehl-Neelsen smear.
• B. GeneXpert MTB/RIF.
• C. Chest radiography.
• D. Tuberculin skin test.

Answer: (B)

A molecular test that directly analyzes the sputum to identify Mycobacterium tuberculosis and also detects rifampin resistance by looking for mutations in the rifampin-resistance determining region of the rpoB gene is used here. This is the GeneXpert MTB/RIF approach, which uses real-time PCR to confirm TB and indicate rifampin resistance within about two hours. Its rapid turnaround and ability to test sputum samples directly make it the best choice for quickly guiding treatment decisions and infection control. Other options don’t provide both TB confirmation and resistance information quickly or at all: Ziehl-Neelsen smear can show acid-fast bacilli but cannot detect drug resistance or confirm TB with high sensitivity on its own; chest radiography is an imaging test that can suggest TB but cannot confirm an active infection or resistance; tuberculin skin testing detects exposure or latent infection, not active TB or drug resistance.