Understanding a Positive Mantoux Test

Niki Salamah

A positive Mantoux test, also known as a tuberculin skin test (TST), indicates that an individual has been exposed to the bacteria that causes tuberculosis (TB). In this article, we will explore what the Mantoux test is, how it is conducted, and what a positive result means.

1. What is the Mantoux Test?

The Mantoux test is a diagnostic tool used to determine if a person has been infected with Mycobacterium tuberculosis, the bacteria that causes tuberculosis. It involves injecting a small amount of purified protein derivative (PPD), which is derived from the TB bacteria, just under the skin’s surface.

2. How is the Mantoux Test Conducted?

The Mantoux test is performed by a healthcare professional. Here are the essential steps involved in the test:

  1. A small amount (0.1 mL) of PPD is injected intradermally into the forearm.
  2. The site of injection is labeled for identification and observed for any initial reactions.
  3. After 48 to 72 hours, the individual returns to have the test site examined.
  4. The healthcare professional measures the size of the skin reaction as an induration (raised, hardened area).
  5. The diameter of the induration is recorded in millimeters.

3. What Does a Positive Mantoux Test Indicate?

A positive Mantoux test means that an individual has been exposed to tuberculosis bacteria and has developed an immune response to the infection. It confirms exposure but does not necessarily indicate active disease.

4. Interpreting a Positive Result

The interpretation of a positive Mantoux test depends on various factors, including the size of the induration. The following criteria are commonly used:

  • ≥ 15 mm: A positive test result in an individual with no known risk factors for TB indicates recent infection or previous BCG vaccination (a TB vaccine).
  • ≥ 10 mm: A positive test result in individuals with risk factors for TB, such as close contact with infected individuals, HIV infection, or conditions that weaken the immune system, indicates latent TB infection (LTBI).
  • ≥ 5 mm: A positive test result in individuals with abnormal chest X-ray findings consistent with previous TB or organ transplants, or those on immunosuppressive therapy, suggests LTBI.
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It’s important to note that a positive Mantoux test alone cannot diagnose active tuberculosis disease. Further evaluations, such as chest X-rays, sputum tests, and clinical assessments, are necessary to determine if active TB infection is present.

5. Follow-Up and Treatment

When a Mantoux test is positive, it is crucial to further evaluate the individual for active TB disease or latent TB infection. Additional tests, as mentioned above, may be performed to assess the individual’s overall health and the status of the infection.

If active TB disease is detected, appropriate treatment with multiple antibiotics will be initiated to prevent the progression of the disease and its transmission to others. In the case of latent TB infection, preventive treatment may be recommended to reduce the risk of future development of active TB disease.


In conclusion, a positive Mantoux test indicates exposure to tuberculosis bacteria and an immune response to the infection. However, it does not solely diagnose active TB disease. Follow-up assessments and further evaluations are necessary to determine the appropriate treatment plan and ensure the individual’s overall health and well-being.

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