True about Mantoux test:
**Core Concept**
The Mantoux test, also known as the tuberculin skin test (TST), is a diagnostic tool for tuberculosis (TB) that measures the body's immune response to purified protein derivative (PPD) of Mycobacterium tuberculosis. It involves injecting a small amount of PPD into the forearm and measuring the resulting skin reaction after 48-72 hours.
**Why the Correct Answer is Right**
The correct answer is based on the principle that a positive reaction to the Mantoux test indicates that the individual has been previously exposed to M. tuberculosis, either through infection or vaccination with the Bacillus Calmette-Guérin (BCG) vaccine. The immune system mounts a response to the PPD, causing an inflammatory reaction at the injection site, which is then measured as a skin induration (hardened area). The size of the induration is directly proportional to the intensity of the immune response. The Mantoux test is particularly useful in diagnosing latent TB infection, which is a critical step in preventing the development of active TB disease.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct criteria for interpreting the Mantoux test results. A positive result is typically defined as an induration of ≥ 10 mm in individuals with recent contact with someone with TB, ≥ 15 mm in HIV-positive individuals, and ≥ 5 mm in individuals with certain medical conditions (e.g., silicosis, fibrotic lung disease, or those taking immunosuppressive therapy).
**Option B:** This option is incorrect because it does not mention the importance of interpreting the Mantoux test results in conjunction with clinical evaluation and other diagnostic tests (e.g., chest X-ray, sputum smear microscopy). A positive result requires careful consideration of the individual's medical history and risk factors for TB.
**Clinical Pearl / High-Yield Fact**
The Mantoux test is not a definitive diagnostic tool and should be used in conjunction with other diagnostic tests and clinical evaluation to confirm the diagnosis of TB. A positive result indicates latent TB infection, which can be treated with antimicrobial therapy to prevent the development of active TB disease.
**Correct Answer:**