Not true about Montoux test
**Core Concept**
The Mantoux test, also known as the tuberculin skin test (TST), is a diagnostic tool used to assess the immune response to Mycobacterium tuberculosis. It involves injecting a small amount of tuberculin into the skin, and the resulting inflammation is measured to determine the presence of tuberculosis (TB) infection.
**Why the Correct Answer is Right**
The Mantoux test works by detecting the delayed-type hypersensitivity reaction, which is mediated by T lymphocytes. When tuberculin is introduced, it triggers the activation of T cells that have previously encountered M. tuberculosis antigens. This activation leads to the release of cytokines, which in turn cause inflammation at the injection site. The size of the induration (not redness) at 48-72 hours is a measure of the individual's immune response to TB.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the Mantoux test is indeed used to screen for latent TB infection, which can progress to active disease if not treated.
* **Option B:** This option is incorrect because the Mantoux test is not a diagnostic tool for other types of infections, such as fungal or viral infections. While it may be used in conjunction with other tests to diagnose TB, it is not a general-purpose diagnostic tool.
* **Option C:** This option is incorrect because the Mantoux test is not a measure of the body's overall immune function. It is a specific test for the immune response to M. tuberculosis antigens.
**Clinical Pearl / High-Yield Fact**
The Mantoux test is often used in conjunction with the interferon-gamma release assay (IGRA) to diagnose latent TB infection. The IGRA is a blood test that measures the release of interferon-gamma in response to M. tuberculosis antigens, and it is often used in individuals who have received the BCG vaccine or have a history of TB exposure.
**Correct Answer:** D.