**Question:** Montoux test is

A. Inoculation of a skin test with a known amount of a tuberculin purified protein derivative (PPD)
B. A diagnostic test for tuberculosis infection
C. Tuberculosis culture on a solid medium
D. Quantiferon test for tuberculosis

**Correct Answer:** A. Inoculation of a skin test with a known amount of a tuberculin purified protein derivative (PPD)

**Core Concept:**
The Montoux test is a skin test used to detect the presence of Mycobacterium tuberculosis antigens in an individual's body. It involves injecting a known amount of tuberculin purified protein derivative (PPD), which is a non-specific mycobacterial antigen, into the skin.

**Why the Correct Answer is Right:**
The Montoux test is rightly A because it involves the inoculation of a skin test with a known amount of tuberculin purified protein derivative (PPD), which is a non-specific mycobacterial antigen that can stimulate a cellular immune response in individuals with previous exposure to Mycobacterium tuberculosis. The test measures the size of the resulting induration (skin reaction) to determine the individual's immune response and the likelihood of tuberculosis infection.

**Why Each Wrong Option is Incorrect:**

B. The Montoux test is not a diagnostic test for tuberculosis infection, but rather a test to evaluate an individual's immune response to M. tuberculosis antigens. A positive test result indicates previous exposure to the bacillus, but it does not confirm a diagnosis of active tuberculosis infection.

C. The Montoux test is not a tuberculosis culture test, as culture is a more definitive test for diagnosing tuberculosis infection. The Montoux test relies on the immune response, while culture confirms the presence of M. tuberculosis.

D. The Montoux test is not a Quantiferon test for tuberculosis, which is a blood test that detects interferon-gamma release by T cells in response to tuberculosis-specific antigens. The Montoux test measures the immune response to non-specific mycobacterial antigens, not tuberculosis-specific antigens.

**Clinical Pearl:**
The Montoux test is a useful tool to assess an individual's immune response to M. tuberculosis antigens. However, it is not a definitive test for tuberculosis infection; a positive test result should be interpreted alongside clinical and radiological findings for a more accurate diagnosis.