Question

Newer MTB antigen-based skin tests (TBSTs).

Hint:

MTB antigen-based skin tests are more reliable than traditional TST in BCG-vaccinated individuals and are especially useful for diagnosing latent TB.

Answer 1

Step 1: Understanding MTB Antigen-Based Skin Tests.
Tuberculosis (T is caused by *Mycobacterium tuberculosis* (MT, and the diagnosis traditionally relies on the Tuberculin Skin Test (TST), also known as the Mantoux test. Newer MTB antigen-based skin tests (TBSTs) have been developed to improve specificity and sensitivity in diagnosing TB infection.
Step 2: Advantages of MTB Antigen-Based Skin Tests.
- Increased Sensitivity and Specificity: Unlike traditional TST, which can result in false positives due to prior BCG vaccination or non-tuberculous mycobacterial infections, newer tests utilize specific MTB antigens to reduce cross-reactivity.
- Simplified Interpretation: TBSTs target unique MTB antigens (e.g., ESAT-6, CFP-10), which are absent in the BCG vaccine strain and non-tuberculous mycobacteria. This improves the accuracy of the test.
- Quicker Results: Some newer tests provide faster results than conventional TST, aiding in timely diagnosis and treatment.
Step 3: Examples of Newer TBSTs.
- Interferon-Gamma Release Assays (IGRAs): These include tests like the QuantiFERON-TB Gold test, which measure the release of interferon-gamma by T-cells when exposed to MTB antigens.
- T-SPOT.TB Test: This test also measures T-cell responses to MTB-specific antigens.
Step 4: Limitations.
Despite the improvements, MTB antigen-based skin tests still have limitations:
- They require sophisticated laboratory facilities.
- They are not definitive for active TB diagnosis and should be used in conjunction with other diagnostic tools like chest X-rays and sputum cultures.