Ppd test how long

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. This will tell doctors whether or not you have TB. TB is a highly 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 persons may react to the TST even though they are not infected with M. The causes of these false-positive reactions may include, but are not limited to, the following:. A TB blood test is the preferred method of testing for people who have received the BCG vaccine in order to prevent false-positive reactions. Some persons may not react to the TST even though they are infected with M.

The reasons for these false-negative reactions may include, but are not limited to, the following:. 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. For example, you may need to have a test if you've been in close contact with someone known to have active TB disease involving the lungs, or if you've recently spent time in a country where TB levels are high. If you've just moved to the UK from a country where TB is common, you should be given information and advice about the need for testing.

Your GP may suggest having a test when you register as a patient. The Mantoux test is a widely used test for latent TB. It involves injecting a small amount of a substance called PPD tuberculin into the skin of your forearm. It's also called the tuberculin skin test TST.