TB Test Practice and Application 5

Question 1

A TST is read at 96 hours instead of the recommended 48–72 hours. The induration measures 8 mm. How should this be handled?

Accepted Answer

Document the late reading with the measurement and note the timing; clinical judgment applies

Answer

Discard the result entirely and repeat immediately

Answer

Automatically classify as negative because readings after 72 hours are invalid

Answer

Classify as positive since induration can only increase over time

Question 2

An employee conversion is defined as a TST change from negative to positive. What minimum increase in induration is typically required to classify a change as a true conversion?

Accepted Answer

An increase of 10 mm or more within a 2-year period

Answer

Any increase from a prior negative result

Answer

An increase of 5 mm from any prior result

Answer

An increase to 15 mm regardless of prior result

Question 3

Which of the following correctly describes the proper disposal of supplies after a TST administration?

Accepted Answer

Discard the uncapped needle directly into a sharps container without recapping

Answer

Recap the needle using a one-handed scoop technique and dispose in a sharps container

Answer

Recap the needle with two hands and discard in a regular waste bin

Answer

Break the needle manually and place in a biohazard bag

Question 4

A healthy US-born adult with no known TB risk factors and no occupational exposure has a TST induration of 14 mm. How is this result classified?

Accepted Answer

Negative; the threshold for low-risk individuals is 15 mm

Answer

Positive; 10 mm is the threshold for all adults

Answer

Positive; 14 mm exceeds the 5 mm high-risk threshold

Answer

Indeterminate; low-risk individuals should use IGRA instead

Question 5

A child recently arrived from a country with high TB prevalence. A TST is ordered. Which additional test is essential if the TST is positive?

Accepted Answer

Chest X-ray to rule out active TB disease

Answer

Sputum acid-fast bacilli smear

Answer

CT scan of the thorax

Answer

Pulmonary function test

Question 6

Which of the following conditions is most likely to cause a false-negative TST result?

Accepted Answer

Severe immunosuppression from HIV infection or chemotherapy

Answer

Recent BCG vaccination within 6 months

Answer

High-dose vitamin C supplementation

Answer

Mild seasonal allergies

Question 7

When documenting a TST result in a patient's medical record, which data elements must be recorded?

Accepted Answer

Date placed, date read, lot number, site, induration in mm, and administering clinician

Answer

Only the induration measurement and date read

Answer

Patient name, date placed, and positive/negative interpretation only

Answer

Date placed and the brand name of tuberculin used