**Question:** Test done for Mycobacterium tuberculosis based on CMI is

A. Tuberculin skin test (Mantoux test)
B. Culture
C. Chest X-ray
D. Biopsy

**Correct Answer:** A. Tuberculin skin test (Mantoux test)

**Core Concept:**
The correct answer is the Tuberculin skin test (Mantoux test) because it is a test for the detection of Mycobacterium tuberculosis-specific immunity, using the purified protein derivative (PPD) of Mycobacterium tuberculosis. Cell-mediated immunity (CMI) plays a crucial role in the immune response against Mycobacterium tuberculosis infection and is assessed through this test.

**Why the Correct Answer is Right:**
The Mantoux test is based on the principle of cell-mediated immunity against Mycobacterium tuberculosis. It is named after the French physician Paul-Maurice Mantoux who first described it in 1908. The test involves injecting a small amount of PPD (purified protein derivative) into the skin, usually in the volar surface of the forearm. The PPD contains a mixture of antigens from Mycobacterium tuberculosis complex and other mycobacteria.

**Why Each Wrong Option is Incorrect:**

A. Culture (B) is an important tool for the isolation and identification of Mycobacterium tuberculosis, but it is not a test for assessing immunity. Culture is used for diagnosing tuberculosis infection or disease by growing the bacteria in a laboratory setting.

B. Chest X-ray (C) is a radiological method used to detect lung abnormalities associated with tuberculosis infection or disease. While it can help in diagnosing tuberculosis, it is not a test assessing immunity against the infection.

C. Biopsy (D) is an invasive procedure to obtain a tissue sample for examination to diagnose tuberculosis. Although it can provide a definitive diagnosis, it is not a test for assessing immunity against the infection.

**Clinical Pearl:**
The tuberculin skin test (Mantoux test) is a simple, non-invasive method to assess cell-mediated immunity against Mycobacterium tuberculosis infection. The test provides an indirect measure of immunity and is helpful in determining the risk of infection or disease, particularly in populations at high risk (e.g., healthcare workers, contacts of tuberculosis patients, and immigrants from endemic areas). A positive test result indicates a higher risk of tuberculosis infection or disease, whereas a negative result indicates a lower risk. However, a negative test result does not rule out tuberculosis infection, as the test takes into account only cell-mediated immunity.

**Explanation:**

The Mantoux test is a crucial tool in tuberculosis diagnosis and risk assessment. The test works by stimulating the immune system and measuring the immune response. When PPD is injected, it triggers a localized immune response, which results in a skin induration (skin reaction). The size of the induration correlates with the degree of cell-mediated immunity against Mycobacterium tuberculosis. A positive test indicates a higher likelihood of tuberculosis infection or disease, while a negative test indicates a lower risk. However, a negative test result does not rule out tuberculosis infection, as it