True about mantoux is –
## **Core Concept**
The Mantoux test, also known as the Tuberculin Skin Test (TST), is a diagnostic tool used to assess if a person has been infected with *Mycobacterium tuberculosis*. It involves the intradermal injection of purified protein derivative (PPD) tuberculin. The test relies on a cell-mediated immune response.
## **Why the Correct Answer is Right**
The correct answer is related to the specifics of how the Mantoux test works and its interpretation. A positive reaction, indicated by induration (not redness), is typically measured after 48-72 hours. The size of the induration is crucial for interpreting the results, with different thresholds used for different populations (e.g., >5 mm in HIV-infected individuals or those with recent exposure, >10 mm in others). A positive result suggests latent TB infection.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Without the specific details of option A, it's challenging to directly address why it's incorrect. However, common misconceptions might include the timing of reading the test (should be 48-72 hours), the measurement of the reaction (induration, not erythema), or the interpretation in specific populations.
- **Option B:** Similarly, without specifics, one might guess that option B could relate to incorrect administration techniques, interpretation criteria, or populations for which the test is not recommended (e.g., those with prior BCG vaccination, though this does not negate the test's utility entirely).
- **Option C:** This option might suggest an incorrect aspect such as using the wrong concentration of PPD or misinterpreting the reaction type (e.g., considering erythema instead of induration).
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Mantoux test does not differentiate between latent TB infection and active TB disease. Also, individuals who have received BCG vaccine may have a false-positive result, though this typically wanes over time. A critical clinical correlation is needed for a positive test result.
## **Correct Answer:** B.