TB Test Diagnostic Approaches 1 — Questions and Answers
Question 1: Which test involves injecting a small amount of tuberculin under the skin to check for a reaction?
- QuantiFERON-TB Gold
- Mantoux Tuberculin Skin Test (TST) (Correct answer)
- Chest X-Ray
- T-SPOT.TB
Correct answer: Mantoux Tuberculin Skin Test (TST)
The Mantoux Tuberculin Skin Test (TST), also known as a PPD test, involves injecting a small amount of tuberculin purified protein derivative (PPD) into the forearm. Healthcare professionals then observe the injection site 48-72 hours later for a raised, hardened area (induration), which indicates a reaction to the tuberculin and suggests past exposure to TB bacteria.
Question 2: Which of the following is an Interferon-Gamma Release Assay (IGRA)?
- Mantoux Tuberculin Skin Test
- Chest X-Ray
- QuantiFERON-TB Gold (Correct answer)
- BCG Vaccine
Correct answer: QuantiFERON-TB Gold
QuantiFERON-TB Gold is an Interferon-Gamma Release Assay (IGRA), which is a blood test used to detect latent tuberculosis infection. Unlike the TST, IGRAs measure the immune system's response to TB-specific antigens in a blood sample, making them a more specific test that is not affected by prior BCG vaccination.
Question 3: What is the purpose of a chest X-ray in TB diagnosis?
- To detect latent TB infection
- To confirm active TB disease (Correct answer)
- To test for TB immunity
- To administer TB treatment
Correct answer: To confirm active TB disease
A chest X-ray is a crucial diagnostic tool used to identify changes in the lungs consistent with active tuberculosis disease. While other tests might indicate exposure or latent infection, the chest X-ray can reveal characteristic lesions, infiltrates, or cavities that suggest the presence of active, symptomatic TB.
Question 4: Which TB test is most appropriate for someone vaccinated with BCG?
- Mantoux Tuberculin Skin Test
- QuantiFERON-TB Gold (Correct answer)
- Skin biopsy
- Sputum smear microscopy
Correct answer: QuantiFERON-TB Gold
The QuantiFERON-TB Gold test is an Interferon-Gamma Release Assay (IGRA) that is highly specific for Mycobacterium tuberculosis. Unlike the Mantoux Tuberculin Skin Test (TST), IGRAs are not affected by prior BCG vaccination, meaning they will not produce a false positive result due to the vaccine, making them ideal for vaccinated individuals.
Question 5: What does a positive Mantoux Tuberculin Skin Test indicate?
- Active tuberculosis disease
- Past exposure to TB or latent infection (Correct answer)
- Immunity to tuberculosis
- Presence of a lung infection
Correct answer: Past exposure to TB or latent infection
A positive Mantoux Tuberculin Skin Test (TST) indicates that a person has been infected with TB bacteria at some point. It does not differentiate between latent TB infection (where the bacteria are present but inactive) and active TB disease. Further tests, like a chest X-ray or sputum culture, are needed to determine if the infection is active.
TB Test Diagnostic Approaches 1
Which test involves injecting a small amount of tuberculin under the skin to check for a reaction?