American Board of Internal Medicine (ABIM) Certification Practice Exam

What induration size is considered positive for tuberculosis testing in certain high-risk patients?

1. 3 mm or larger

2. 5 mm or larger

3. 10 mm or larger

4. 15 mm or larger

The correct answer is: 5 mm or larger

A result of 5 mm or larger is considered positive for tuberculosis testing, particularly in certain high-risk patients. These high-risk groups include individuals with recent close contact with a person with infectious tuberculosis, those with HIV infection, individuals who have had an organ transplant or are immunocompromised, and patients with certain other medical conditions that increase their susceptibility to tuberculosis. In these populations, a smaller induration size is necessary to trigger suspicion for active tuberculosis due to their increased likelihood of progression from latent TB infection to active disease. This guideline reflects the need to be more vigilant with those who have diminished immune responses, as even a minimal exposure can lead to severe consequences in these groups. Greater induration sizes, such as 10 mm or 15 mm, are generally indicated for healthy individuals or those at lower risk, making the 5 mm threshold particularly critical for maximizing the early identification and treatment of tuberculosis in the most vulnerable patients.