Which test for tuberculosis tests for active TB infection?

• A. Mantoux test
• B. PPD test
• C. Chest X-ray
• D. QuantiFERON-TB Gold test

Answer: (D)

Testing for tuberculosis infection falls into two categories: tests that show an immune response to TB and tests that look for actual bacterial activity in the body. The QuantiFERON-TB Gold is an interferon-gamma release assay that indicates TB infection, but it cannot distinguish latent infection from active TB disease. The Mantoux skin test (PPD) works the same way—it's a marker of exposure, not proof of active disease. A chest X-ray may reveal signs suggestive of active TB, such as infiltrates or cavities, but it isn’t definitive for diagnosing infection or confirming active disease. To prove active TB, you need microbiologic confirmation from respiratory samples (smear microscopy, culture, or nucleic acid amplification tests) along with clinical and radiographic correlation. So, none of these tests uniquely tests for active TB on its own; diagnosing active TB relies on microbiology plus imaging and clinical assessment.