Tuberculin Skin Test
How It Is Done
For a tuberculin skin test, you sit
down and turn the inner side of your forearm up. The skin where the test is
done is cleaned and allowed to dry. A small shot of the TB antigen (purified
protein derivative, or PPD) is put under the top layer of skin . The fluid makes
a little bump (wheal) under the skin. A circle may be drawn around the test
area with a pen.
Do not cover the site with a bandage. You must see
your doctor 2 to 3 days after the test to have the skin test checked.
How It Feels
You may feel a quick sting or pinch from
There is a very slight risk of having a severe
reaction to the tuberculin skin test, especially if you have had tuberculosis
allergic reaction can cause a lot of swelling and pain
at the site. A sore may be present.
You cannot get a TB infection
from the tuberculin skin test, because no live bacteria are used for the
After the test
Some redness at the skin test site
is expected. The site may itch, but it is important that you do not scratch it,
since this may cause redness or swelling that could make it hard to read the
skin test. If itching is a problem, put a cold washcloth on the site and then
A strong positive reaction may cause mild pain. Talk to
your doctor if you have:
A tuberculin skin test is done to see if
you have ever had
tuberculosis (TB) (infection with Mycobacterium tuberculosis).
Redness alone at the skin test
site usually means you have not been infected with TB bacteria. A firm red bump
may mean you have been infected with TB bacteria at some time. The size of the
firm bump (not the red area) is measured 2 to 3 days after the test to
determine the result. Your doctor will consider your chance of having TB when
looking at the skin test site.