TB Test Practice and Application 2

Question 1

A TST is placed on a patient who received BCG vaccination as a child. The induration measures 12 mm. What is the correct interpretation?

Accepted Answer

Disregard BCG history; 12 mm is positive for a standard-risk person

Answer

The result is negative because BCG causes false positives

Answer

The result must be confirmed with a chest X-ray before reading

Answer

BCG vaccination automatically invalidates the TST result

Question 2

Which anatomical site is the standard location for placing a TST (Mantoux test)?

Accepted Answer

Volar surface of the forearm

Answer

Deltoid muscle

Answer

Dorsal surface of the forearm

Answer

Antecubital fossa

Question 3

A healthcare worker's TST shows 9 mm induration. She has no known risk factors. How should this result be classified?

Accepted Answer

Negative, because the threshold for healthcare workers is 10 mm

Answer

Positive, because any induration in a healthcare worker is significant

Answer

Positive, because the threshold is 5 mm for all tested individuals

Answer

Indeterminate; repeat in 1–3 weeks

Question 4

What is the recommended needle gauge for administering a Mantoux tuberculin skin test?

Accepted Answer

26–27 gauge

Answer

18–20 gauge

Answer

22–23 gauge

Answer

30 gauge

Question 5

After correctly placing a TST, the nurse observes no bleb (wheal) at the injection site. What action is most appropriate?

Accepted Answer

Repeat the test immediately at a site at least 2 inches from the first

Answer

Document the result as 0 mm and schedule a 48–72 hour reading

Answer

Apply pressure to encourage bleb formation

Answer

Report the result as invalid and do not repeat for 4 weeks

Question 6

A patient with HIV has a TST induration of 4 mm. How should this result be interpreted?

Accepted Answer

Positive; HIV-positive individuals use a 5 mm threshold

Answer

Negative; the threshold for HIV-positive individuals is 5 mm

Answer

Negative; HIV-positive individuals use a 10 mm threshold

Answer

Positive; any reaction in an HIV-positive patient is significant

Question 7

Which scenario best illustrates the 'booster phenomenon' in TST testing?

Accepted Answer

A second TST 1–3 weeks after a negative first TST shows increased induration

Answer

A patient develops a large blister at the TST site indicating allergy

Answer

Repeated TST tests permanently sensitize a patient to tuberculin

Answer

A TST result reverts from positive to negative over several years