Question

Upon performing a Mantoux tuberculin skin test, a 15-mm zone of induration is observed. The patient has a normal chest X-ray and does not report feeling ill. The vaccination history of the patient is unknown. Which of the following scenarios explains the patient's test results, given her case history? To be marked correct, you'll need to select all applicable statements, as there may be more than one correct answer.

- The patient has latent tuberculosis.
- The patient has been vaccinated against tuberculosis.
- The tuberculin skin test was defective; the test should be repeated using less purified tuberculin antigen.
- The patient has an active case of tuberculosis.

Answer 1

A 15-mm zone of induration in a Mantoux tuberculin skin test with normal X-ray and no illness symptoms can indicate either latent tuberculosis or previous vaccination.

Step-by-step explanation:

A 15-mm zone of induration observed in a Mantoux tuberculin skin test indicates a positive result. Given the patient's normal chest X-ray and lack of illness symptoms, there are several possible scenarios that can explain these test results:

1. The patient has latent tuberculosis (TB): Latent TB is characterized by a positive immune response to TB bacteria but no active infection or symptoms.
2. The patient has been vaccinated against TB: Vaccination with the BCG vaccine can cause false-positive results on the tuberculin test.
3. The patient has an active case of TB: Although the patient does not report feeling ill, it is still possible to have an active infection without exhibiting symptoms.

It is not possible to determine the patient's vaccination history from the given information, so both scenarios 1 and 2 could explain the test results. However, the test should not be considered definitive for diagnosing active TB, and additional evaluation is needed.