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 the needle.
There is a very slight risk of having a severe reaction to the tuberculin skin test, especially if you have had tuberculosis (TB). An 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 test.
A tuberculin skin test is safe for pregnant or breast-feeding women.
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 dry it.
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.