Which statement is the primary purpose of the interferon-gamma release assay (IGRA) in TB testing?

• A. To detect latent TB infection, particularly in people previously vaccinated with BCG.
• B. To diagnose active TB in symptomatic individuals only.
• C. To confirm HAV infection.
• D. To detect HIV infection.

Answer: (A)

IGRA is a blood test that measures the immune system’s response to TB-specific antigens. It detects latent TB infection by detecting T cells that release interferon-gamma when exposed to these TB-focused antigens, which are not present in the BCG vaccine. Because these antigens are not shared with BCG, IGRA reduces false positives in people who’ve been vaccinated, making it more specific for TB infection in that population. A positive result indicates prior TB infection and helps identify individuals who may benefit from preventive treatment, but it cannot distinguish latent infection from active TB on its own; further clinical evaluation and microbiological testing are needed to assess active disease. This test is not used to diagnose HAV or HIV.