American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the preferred screening test for Mycobacterium tuberculosis infection for patients unlikely to return for follow-up?

1. Skin test

2. Interferon-γ release assay

3. Sputum culture

4. Chest X-ray

The correct answer is: Interferon-γ release assay

For patients who are unlikely to return for follow-up, the preferred screening test for Mycobacterium tuberculosis infection is the interferon-γ release assay (IGRA). This test is more advantageous in this context because it is a blood test that does not require the patient to return for readings, which is necessary with the tuberculin skin test (TST). The IGRA measures the immune response to specific TB antigens, providing results that are not subject to interpretation based on the measurement of induration, as seen with the skin test. This feature makes the IGRA particularly useful in circumstances where ensuring patient adherence to follow-up is a concern. Additionally, the IGRA is less affected by prior Bacillus Calmette–Guérin (BCG) vaccination and does not require differentiation of induration size based on patient risk factors, adding to its utility in diverse populations. Other screening methods, such as sputum cultures and chest X-rays, are not first-line tests for screening latent TB infection but rather for diagnosing active tuberculosis disease. Therefore, they are not appropriate choices when the goal is to screen for latent infection without the need for a follow-up visit.