A patient with a chronic cough is given a tuberculin skin test, which when properly read has a zone of induration greater than 15 mm. What does this mean?

Question

Quizplus · Accepted Answer

The tuberculin test indicates previous infection with Mycobacterium tuberculosis or Mycobacterium bovis from between several weeks to 5 years. It does not provide proof of current active infection with M. tuberculosis. The tuberculin test detects cell-mediated immunity and not antibody. If a person is infected with a nontuberculous strain of mycobacteria, usually the skin reaction is smaller. Specific skin tests for some of these nontuberculous strains of mycobacteria are available. Vaccination with bacillus Calmette-Guérin (BCG) vaccine should not result in this large a zone of induration. The newer whole blood interferon-gamma release assays (IGRAs), which also do not distinguish latent tuberculosis infection from tuberculosis disease, are superior to distinguish infected from BCG vaccinated.

A Patient with a Chronic Cough Is Given a Tuberculin