Tuberculosis test

What is tuberculosis?

To know more about the tuberculosis test, we must first start knowing the disease.

Tuberculosis (abbreviated TB or TB), alternatively and historically called tuberculosis, is a contagious bacterial infection that mainly affects the lungs, but can spread to other organs. The most important and representative bacterial species causing tuberculosis is Mycobacterium tuberculosis or Koch bacillus, belonging to the Mycobacterium tuberculosis complex.

Tuberculosis is possibly the most prevalent infectious disease in the world. Considering its latent form, in which it does not present symptoms, it is estimated that it affects 33% of the world population. It is also the second cause of death globally, and the first among infectious diseases.

Types of tests to detect tuberculosis bacteria

Two types of tests are used to detect tuberculosis bacteria in the body: the tuberculin skin test and blood tests. A positive result on the tuberculin skin test or a blood test only indicates that the person has been infected with TB bacteria. It does not indicate if the person has latent tuberculosis infection (LTBI) or if it has evolved to tuberculosis disease. To determine if the person has TB disease, it is necessary to do other tests, such as a chest x-ray or take a sputum sample.

Cutaneous or Mantoux test

The tuberculin skin test is also called the Mantoux test. The tuberculin skin test requires two visits to the health care provider. In the first visit, the test is done, and in the second, the health care provider analyzes its results.

The tuberculin skin test is done by injecting a small amount of fluid called tuberculin into the skin of the lower arm.

The person who is having the tuberculin skin test must return within 48 to 72 hours for a trained health worker to examine the reaction in the arm.

The result of this skin test depends on the size of the raised, hardened, or swollen area.

A positive reaction to the skin test means that the body of the person is infected with tuberculosis bacteria.

More tests are needed to determine if the person has latent tuberculosis infection or tuberculosis disease.

A negative reaction to the skin test means that the body of the person has not reacted to the test and is not likely to have latent tuberculosis infection or tuberculosis disease.

The tuberculin skin test can be repeated without problems, but if it is repeated, the new test should be done in another part of the body (e.g., in the other arm).


If a person is found to be infected with tuberculosis bacteria, more tests should be done to see if they have latent tuberculosis infection or tuberculosis disease.

Who should be screened?

Certain people should be tested for tuberculosis infection because they are at higher risk of being infected with the bacteria that cause it. Among these people are the following:

  • People who have spent time with someone who has TB disease.
  • People who come from a country where tuberculosis is common (most of the countries of Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia).
  • People who live or work in high-risk environments (for example, correctional facilities, long-term care centers or nursing homes and shelters for the homeless).
  • Health workers who care for patients at higher risk of contracting TB disease.
  • Babies, children, and adolescents exposed to adults who are at higher risk of infection with latent tuberculosis or tuberculosis disease.

Many people who have latent tuberculosis infection never have tuberculosis disease. But some people who have latent TB infection are more likely than others to have TB disease.


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