Mantoux test facts for kids

The Mantoux test is a special skin test used to check if someone has been exposed to the bacteria that cause tuberculosis. Tuberculosis is a serious lung disease.

In the late 1800s, a scientist named Robert Koch discovered a substance called tuberculin. He hoped it would cure tuberculosis. Even though it didn't work as a cure, tuberculin became very useful for finding out if someone had been near the tuberculosis bacteria. Tuberculin is made from parts of the bacteria that cause the disease.

Later, a French physician named Charles Mantoux used Koch's discovery to create the Mantoux test. This test helps doctors see how a person's immune system reacts to tuberculin.

How the Test Works

The Mantoux test involves injecting a tiny amount of tuberculin just under the skin, usually on the forearm. After 48 to 72 hours (about 2 to 3 days), a healthcare worker checks the injection site. They look for a raised, firm bump, which is called an induration. The size of this bump helps determine the test result. Redness around the area is not measured.

Understanding the Results

Positive Test Result

If the test shows a positive result, it means your immune system has come into contact with Mycobacteria, which are the bacteria that cause tuberculosis. However, a positive result does not always mean you have an active tuberculosis infection. It could mean:

• You have been infected with tuberculosis bacteria in the past.
• You have a latent (sleeping) tuberculosis infection, meaning the bacteria are in your body but not making you sick.
• You have received the BCG vaccine, which is a vaccine for tuberculosis.

Sometimes, a test can show positive even when it should be negative. This is called a false positive.

Negative Test Result

A negative test result usually means you have not been infected with tuberculosis bacteria.

However, sometimes a test can show negative even when it should be positive. This is called a false negative. This can happen if:

• Your immune system is weak. For example, people with conditions like HIV might have an immune system that is too weak to react to the test.
• You are taking certain medicines, like steroids, which can weaken your immune system's reaction.

Images for kids

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  The size of induration is measured 48–72 hours later. Erythema (redness) should not be measured.

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  Mantoux test injection site in a subject without chronic conditions or in a high-risk group clinically diagnosed as negative at 50 hours

See also

In Spanish: Prueba de Mantoux para niños