TB Test Practice and Application 3

Question 1

A clinician orders an IGRA (QuantiFERON-TB Gold Plus) for a patient who had a BCG vaccine abroad. What is the primary advantage of IGRA over TST in this case?

Accepted Answer

IGRA is not affected by prior BCG vaccination

Answer

IGRAs measure interferon-gamma release in response to TB-specific antigens (ESAT-6 and CFP-10) not present in BCG, so prior BCG vaccination does not cause false-positive IGRA results.

Question 2

When reading a TST result, the clinician should measure which physical finding?

Accepted Answer

The diameter of induration (palpable raised area)

Answer

Only the diameter of induration—the firm, palpable swelling—is measured, not the surrounding redness (erythema).

Question 3

A 4-year-old child is a close contact of a confirmed active TB case. Her TST measures 6 mm. What is the correct interpretation?

Accepted Answer

Positive; close contacts of active TB use the 5 mm threshold

Answer

For close contacts of active TB cases, a TST of 5 mm or more is considered positive regardless of age.

Question 4

Which of the following is a contraindication to performing a TST?

Accepted Answer

A previously documented positive TST result

Answer

A previously documented positive TST is a contraindication to repeat TST, as severe local reactions (necrosis, ulceration) can occur.

Question 5

A patient's TST bleb measures 6 mm immediately after injection. At the 72-hour reading, induration measures 12 mm. Which measurement is recorded as the official result?

Accepted Answer

12 mm — the induration at the 48–72 hour reading

Answer

The official TST result is the induration measured at the 48–72 hour reading, not the immediate post-injection bleb.

(TB Test) Tuberculosis Test Certification Practice Test

(TB Test) Tuberculosis Test Certification Practice Test

TB Test Practice and Application 3