Which test is preferred to assess latent TB infection in someone who has received BCG vaccination?

Which test is preferred to assess latent TB infection in someone who has received BCG vaccination?

• A. Interferon-gamma release assay (IGRA).
• B. Purified protein derivative (PPD) tuberculin skin test.
• C. Chest x-ray.
• D. Sputum acid-fast smear.

Answer: (A)

In someone who has received BCG, testing for latent TB infection relies on a test that isn’t affected by vaccination. The interferon-gamma release assay uses TB-specific antigens that are not present in the BCG vaccine, so it’s much more specific in this group and fewer false positives occur compared with the PPD tuberculin skin test. A positive IGRA indicates latent TB infection and prompts further evaluation and possible treatment, depending on risk factors. Chest X-ray is used to look for signs of active TB disease rather than latent infection, and a sputum smear detects bacteria in active pulmonary TB, not latent infection.

In someone who has received BCG, testing for latent TB infection relies on a test that isn’t affected by vaccination. The interferon-gamma release assay uses TB-specific antigens that are not present in the BCG vaccine, so it’s much more specific in this group and fewer false positives occur compared with the PPD tuberculin skin test. A positive IGRA indicates latent TB infection and prompts further evaluation and possible treatment, depending on risk factors. Chest X-ray is used to look for signs of active TB disease rather than latent infection, and a sputum smear detects bacteria in active pulmonary TB, not latent infection.