A tuberculin skin test is done to see if you have ever had tuberculosis (TB) (Mycobacterium tuberculosis). It is done by putting a small amount of TB protein (antigens) under the top layer of skin on your inner forearm. If you have ever been exposed to the TB bacteria, your skin will react to the antigens by developing a firm red bump at the site within 2 days.

The Mantoux skin test uses TB antigens called purified protein derivative (PPD). The test cannot tell if the infection is active or inactive (latent).

The Mantoux test uses a measured amount of PPD in a shot that is put under the top layer of skin on your forearm. A Mantoux test is a good test for a TB infection. It is often used when symptoms, screening, or testing, such as a chest X-ray, show that a person may have TB.

A tuberculin skin test cannot tell how long you have been infected with TB or if the infection can be passed to others (active TB).

Why It Is Done

A tuberculin skin test is done to find people with tuberculosis (TB), including:

• People who have been in close contact with someone known to have TB.
• Health care workers who are likely to be exposed to TB.
• People with TB symptoms, such as an ongoing cough, night sweats, and weight loss for no reason.
• People who have had an abnormal chest X-ray.
• People who have had a recent organ transplant or with impaired immune systems, such as those with human immunodeficiency virus (HIV).

A tuberculin skin test should not be done for people who have a:

• Known TB infection.
• Positive tuberculin skin test in the past. A second test may cause a more severe reaction to the TB antigens.
• Skin rash that would make it hard to read the skin test.

How To Prepare

Before having a tuberculin skin test, tell your health professional if you:

• Have symptoms of tuberculosis (TB), such as an ongoing cough, night sweats, or weight loss for no reason.
• Have had a positive tuberculin skin test in the past.
• Have had TB in the past.
• Have risk factors for TB. Risk factors include:
  • Contact with a person who has TB.
  • A job as a health care worker that may cause you to be exposed to people with TB.
  • Having lived or traveled in a country where TB is common.
• Have been given a TB vaccination. The vaccine contains a bacteria called BCG (bacille Calmette-Guérin) that is closely related to the bacteria that cause TB.
• Have been treated with medicines, such as corticosteroids, that can affect your immune system.
• Are infected with the human immunodeficiency virus (HIV).
• Have a skin rash that may make it hard to read the skin test.

Talk to your health professional about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will indicate. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).