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Tests and Procedures

TB Screening (Skin) 

Does this test have other names?

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

What is this test?


Why do I need this test?


Symptoms of TB include:

  • Cough

  • Fever

  • Night sweats

  • Weight loss


You also might have this test if you:

  • Have HIV or another disease that weakens your immune system

  • Use illegal drugs


If you are a health care worker, you might have this test periodically as part of your facility's infection control program. Testing for TB is often part of routine prenatal care.

What other tests might I have along with this test?

If you test positive on a TB skin test, your doctor will probably order a chest X-ray, sputum smear (a test on mucus you cough up), and TB culture to confirm the results. 

What do my test results mean?


The test may be interpreted as positive if the skin where you were injected is hard, raised, red, and swollen. However, redness alone is not considered a positive reaction.

A positive skin test means it's likely that you were infected with TB bacteria at some point in time, but this does not necessarily mean that you have an active TB infection.

In many cases, if you have a healthy immune system, your body will "wall off" the TB bacteria soon after you are infected, and you will not go on to develop an active TB infection. Further tests are necessary to see if you have active or inactive TB.

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

How is this test done?

Your inner forearm is disinfected and a small amount of fluid called tuberculin is injected into your skin. 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 to be examined by a trained health care worker.

Does this test pose any risks?


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 don't have, or never had, a TB infection.

You might have a false negative test if you are:

  • Malnourished

  • On steroid therapy

  • Taking drugs that can affect your immune system, such as medication for AIDS or cancer

How do I get ready for this test?


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