TB Test Core Knowledge and Fundamentals 4

Question 1

The Mantoux test is read by measuring:

Accepted Answer

The diameter of induration (palpable raised area), not redness

Answer

Only the firm, raised induration is measured in millimeters transversely to the forearm; erythema alone is not significant.

Question 2

A nurse accidentally injects tuberculin subcutaneously instead of intradermally. What is the correct action?

Accepted Answer

The test is invalid and must be repeated at a different site

Answer

Subcutaneous injection results in rapid absorption and no wheal formation, invalidating the test; it must be repeated at a different site after waiting.

Question 3

Which high-risk group uses a ≥5 mm induration cutoff for a positive TST?

Accepted Answer

HIV-positive individuals

Answer

People with HIV, recent close contacts of TB cases, and those with fibrotic changes on chest X-ray use the lowest (≥5 mm) positive threshold.

Question 4

What is the window period from TB exposure to when a TST becomes reliably positive?

Accepted Answer

2–8 weeks after exposure

Answer

Immune sensitization after M. tuberculosis infection takes 2–8 weeks, so TST and IGRA may be negative if done too soon after exposure.

Question 5

Which of the following conditions can cause a false-negative TST result?

Accepted Answer

Severe immunosuppression

Answer

Severely immunosuppressed individuals (e.g., HIV with low CD4, on high-dose steroids) may be anergic and unable to mount a delayed hypersensitivity response.

(TB Test) Tuberculosis Test Certification Practice Test

(TB Test) Tuberculosis Test Certification Practice Test

TB Test Core Knowledge and Fundamentals 4