Minus Related Pages. Reading the result of a TB skin test. To receive email updates about this page, enter your email address: Email Address. What's this? Links with this icon indicate that you are leaving the CDC website. Most persons can receive a TST. TST is the recommended method of testing for children younger than 5 years of age. TST is contraindicated only for persons who have had a severe reaction e. It is not contraindicated for any other persons, including infants, children, pregnant women, or persons living with HIV.
In general, there is no risk associated with repeated tuberculin skin test placements. If a person does not return within hours for a tuberculin skin test reading, a second test can be placed as soon as possible.
A boosted reaction occurs mainly in previously infected, older adults whose ability to react to tuberculin has decreased over time. When given a TST years after infection, these persons may have an initial negative reaction. However, the TST may stimulate the immune system, causing a positive or boosted reaction to subsequent tests.
Vaccination with live viruses, including measles, mumps, rubella, oral polio, varicella, yellow fever, BCG, and oral typhoid, may interfere with TST reactions. For persons scheduled to receive a TST, testing should be done as follows:.
There are two kinds of tests that are used to determine if a person has been infected with TB bacteria: the TB blood test and the TB skin test. The tests measure the response of TB proteins when they are mixed with a small amount of blood.
Only one visit is required to draw blood for this test. Health care providers are encouraged to use newer TB blood tests to screen for TB infection. In order to prevent false-positive reactions, TB blood tests are also the preferred method of TB testing for people 5 years of age and older who have received the BCG TB vaccine.
A diagnosis of latent TB infection is made if a person has a positive TB test result and a medical evaluation does not indicate TB disease. TB disease is diagnosed by medical history, physical examination, chest x-ray, and other laboratory tests.
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.
Tuberculosis is a highly contagious bacterial disease. 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. It most often affects the lungs. The bacteria can remain inactive dormant in the lungs for many years. This situation is called latent TB.
Most people in the United States who are infected with the bacteria do not have signs or symptoms of active TB. A negative reaction usually means you have never been infected with the bacteria that cause TB. With a negative reaction, the skin where you received the PPD test is not swollen, or the swelling is very small. This measurement is different for children, people with HIV, and other high-risk groups.
The PPD skin test is not a perfect screening test. A few people infected with the bacteria that cause TB may not have a reaction. Also, diseases or medicines that weaken the immune system may cause a false-negative result.
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