TB Test Assessment and Evaluation 3

Question 1

A QuantiFERON-TB Gold Plus (QFT-Plus) test reports TB1 and TB2 tube results. What is the significance of the TB2 tube?

Accepted Answer

It detects both CD4+ and CD8+ T-cell responses, potentially improving detection in some populations

Answer

It detects CD4+ T-cell response only, improving sensitivity in immunocompromised patients

Answer

It replaces the nil tube to reduce background interference

Answer

It measures IgG antibody levels against ESAT-6 and CFP-10

Question 2

A nurse administers 0.1 mL of PPD tuberculin intradermally and observes a bleb of 6mm immediately after injection. What does this bleb indicate?

Accepted Answer

Correct intradermal injection technique with proper bleb formation

Answer

The test is invalid and must be immediately reinjected at a different site

Answer

Subcutaneous injection occurred and the site should be marked for reading

Answer

The patient is likely sensitized and will have a large induration

Question 3

Which of the following populations has the LOWEST positive predictive value for TST, making IGRA generally preferred?

Accepted Answer

BCG-vaccinated individuals from countries with routine infant BCG programs

Answer

Foreign-born persons from high-TB-burden countries

Answer

HIV-positive individuals with CD4 count >500 cells/µL

Answer

Household contacts of a confirmed active TB case

Question 4

A patient's TST placed on Monday is read on Friday (96 hours later). The result shows 12mm induration. How should this be handled?

Accepted Answer

Reject the result as invalid; repeat TST immediately at a new site

Answer

Accept the result as positive since induration is present

Answer

Document as negative since reading beyond 72 hours is unreliable

Answer

Request IGRA to confirm before making any clinical decision

Question 5

In a correctional facility outbreak investigation, a newly incarcerated individual tests positive on TST. Which factor is most important in determining whether this represents LTBI acquired inside or before incarceration?

Accepted Answer

Documentation of a negative TST at intake within the past 2 years

Answer

The size of the induration in millimeters

Answer

The inmate's country of origin

Answer

The presence or absence of BCG vaccination scar

Question 6

When performing a contact investigation for a smear-positive pulmonary TB case, which contacts should be prioritized for immediate TST or IGRA testing?

Accepted Answer

Close contacts sharing the same household or enclosed workspace for extended periods

Answer

Casual contacts with <1 hour cumulative exposure in outdoor settings

Answer

All individuals who have ever met the index case socially

Answer

Only contacts who report symptoms of cough or fever

Question 7

A patient previously treated for active TB disease presents with a positive TST. What is the appropriate interpretation?

Accepted Answer

Expected positive result; TST remains positive after prior TB or LTBI treatment

Answer

Reinfection with a new TB strain requiring full workup

Answer

False positive due to residual immune memory from BCG

Answer

LTBI requiring immediate treatment initiation