Tuberculin Skin Test
A tuberculin skin test is done to see if
you have ever had
tuberculosis (TB). The test 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 (Mycobacterium tuberculosis), your skin will react to the
antigens by developing a firm red bump at the site within 2 days.
The TB antigens used in a tuberculin skin test are called purified
protein derivative (PPD). A measured amount of PPD in a shot is put under the
top layer of skin on your forearm. This is a good test for finding a TB
infection. It is often used when symptoms, screening, or testing, such as a
X-ray, show that a person may have TB.
tuberculin skin test cannot tell how long you have been infected with TB. It
also cannot tell if the infection is
latent (inactive) or is active and can be passed to
Why It Is Done
A tuberculin skin test is done to find
people who have 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 unexplained weight loss.
- People who have had an
abnormal chest X-ray.
- People who have had a recent organ transplant
or have an
impaired immune system, such as those with
human immunodeficiency virus (HIV).
A tuberculin skin test should not be done for
- With a known TB infection.
- Who have
had a previous severe reaction to the TB antigens.
- Who have a skin rash
that would make it hard to read the skin test.
How To Prepare
Before having a tuberculin skin test,
tell your doctor if you:
- Have symptoms of tuberculosis (TB), such as an
ongoing cough, night sweats, or unexplained weight loss.
- Have had
a severe reaction to a tuberculin skin test in the past.
- Have had
TB in the past.
- Have risk factors for TB, which are things that increase your risk. Risk factors for TB include:
- Contact with a person who has
- 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
- Have been given a TB vaccination. The vaccine
contains a bacteria called BCG (bacille Calmette-Gu�rin) that is
closely related to the bacteria that cause TB.
- Have been treated
with medicines, such as
corticosteroids, that can affect your
- 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 doctor about any concerns you have regarding
the need for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).