TB Screening (Skin) | Northwestern Medicine (2024)

Does this test have other names?

Tuberculin test, TST, Mantoux skin test, PPD (purified protein derivative)

What is this test?

This test shows if you have been infected with tuberculosis (TB). TB is a very contagious bacterial infection that is spread through the air. It's possible to have inactive (latent) TB and not feel sick or have noticeable symptoms. Or you can have active TB disease with symptoms. People with latent TB are not contagious.

Why do I need this test?

You may need this test if you have recently been exposed to someone who has TB. Or you may need it if your healthcare provider thinks you may have a TB infection.

Symptoms of TB may include:

• Cough

• Fever

• Night sweats

• Unexplained weight loss

• Coughing up blood

• Chest pain

• Fatigue

• Shortness of breath

TB usually affects the lungs. But it can spread to other parts of your body, including your joints, spine, brain, and kidneys. It can then cause other symptoms.

You also might have this test if you:

• Have HIV or another disease that weakens your immune system

• Use illegal drugs

• Live or work in a place with a higher rate of TB infection, such as a prison or nursing home

• Need to start a medicine that suppresses your immune system

• Recently emigrated or traveled to areas where TB is more common, such as some Eastern European or Latin American countries

• Are a healthcare worker and need this test as part of your facility's infection control program

• Are pregnant and having routine prenatal care tests

What other tests might I have along with this test?

If you test positive on a TB skin test, you will also likely need a chest X-ray, sputum smear (a test on mucus you cough up), and TB culture. These tests areto find out if you have active or latent TB.A blood screening test is also available for TB. But your healthcare provider will advise only one screening test based on your case.

How is this test done?

A small amount of fluid called tuberculin is injected under the skin on your inner forearm. A circle is drawn around the injection site with long-lasting ink. You need to return to the testing site after 48 to 72 hours. A healthcare provider will check the area where the injection was done for a reaction.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

A positive test result means you may have been infected with TB at some point. It does not mean you have an active TB infection. The test may be seen as positive if the skin where you were injected is hard, raised, red, and swollen. But redness alone is not considered a positive test result.

In many cases, a healthy immune system will surround the TB bacteria soon after you are infected. This means you will not go on to have an active TB infection. You will need more tests to see if you have active or inactive TB.

If you have no reaction, then the skin test is negative. You are not likely to have inactive TB or TB disease.

Does this test pose any risks?

When the needle pricks your arm, you may feel a slight sting or pain. Afterward, the site may be sore.

You cannot get TB from the skin test.

What might affect my test results?

If you have been vaccinated against tuberculosis with Bacilli Calmette-Guerin (BCG), you can have a positive reaction to the skin test even if you never had a TB infection.

You might have a false negative test if you are:

• Malnourished

• On steroid therapy

• Taking medicines that can affect your immune system, such as medicine for AIDS or cancer

How do I get ready for this test?

You don't need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.