At the first visit, the provider will clean an area of your skin, usually the inside of your forearm. You will get a small shot injection that contains PPD.
The needle is gently placed under the top layer of skin, causing a bump welt to form. This bump usually goes away in a few hours as the material is absorbed. After 48 to 72 hours, you must return to your provider's office. Your provider will check the area to see if you have had a strong reaction to the test. Tell your provider if you have ever had a positive PPD skin test. If so, you should not have a repeat PPD test, except under unusual circumstances. Tell your provider if you have a medical condition or if you take certain medicines, such as steroids, which can affect your immune system.
These situations may lead to inaccurate test results. Tell your provider if you have received the BCG vaccine and if so, when you received it. This vaccine is only given outside of the United States. This test is done to find out if you have ever come in contact with the bacteria that cause TB. TB is an easily spread contagious disease. However, the disease is relatively rare in the United States. You should get a PPD skin test if you work in the healthcare field. All healthcare workers must be routinely screened for TB.
A doctor or nurse will swab the skin of your inner forearm with alcohol. You may feel a slight sting. A bump or small welt will form, which usually goes away in a few hours. The amount of swelling may be different for children, people with HIV, the elderly, and others at high risk. A small reaction, called an induration , at the site of the test 5 to 9 millimeters of firm swelling is a positive result in people who:.
More tests are necessary to confirm the diagnosis. For people without a known risk factor for TB, a 15 mm or larger firm swelling at the injection site indicates a positive reaction. Your doctor will follow up on positive results with a chest X-ray, a CT scan , and a sputum test that looks for active TB in the lungs. Some people infected with the bacteria that cause TB may not have any reaction to the test.
Diseases such as cancer and medications like steroids and chemotherapy that weaken your immune system may also cause a false-negative result. A tuberculin skin test cannot tell how long you have been infected with TB. It also cannot tell if the infection is latent inactive or if you have active TB that can be passed to others. 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 tuberculosis 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. There is a very slight risk of having a severe reaction to the tuberculin skin test, especially if you've had tuberculosis TB. An allergic reaction can cause a lot of swelling and pain at the site.
You may have a sore. You cannot get a TB infection from the tuberculin skin test. That's because no live bacteria are used for the test. Redness alone at the skin test site usually means you haven't 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 find out the result.
Your doctor will consider your chance of having TB when looking at the skin test site. Results of the test depend on your risk for TB. If you are in a high-risk group, a smaller bump is considered a sign of infection. Tuberculosis TB. Section Navigation. Facebook Twitter LinkedIn Syndicate. Testing for TB Infection. Minus Related Pages.
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