![]() More tests-such as a chest X-ray, a sputum culture, or both-are usually done to see if you have an active TB infection. Here is an excerpt from the CDC website on tuberculin testing: Positive TB blood test: This means that the person has been infected with TB bacteria. Inform your patient if the test is positive or negative. If you tested positive, just to be sure it’s safe, there should be a follow-up with your provider. It also can't tell the difference between a TB infection and a TB vaccination ( BCG vaccination). A measurement of more than 5 mm could be considered a positive result. The test can't tell whether you have active or inactive (latent) TB. For more information, please see the CDC Testing and Diagnosis webpage. Your doctor will take a blood sample from your arm for testing and you will be able to know your test results within few days. If you have no skin reaction the result is negative, which means you. No firm bump forms at the test site, or a bump forms that is smaller than 5 mm (0.2 in.)Ī firm bump that is 5 mm (0.2 in.) or larger in size suggests a TB infection.Ī positive reaction can usually be seen for about 1 week.Ī positive tuberculin skin test doesn't mean you have contagious (active) TB. The TB blood test is the recommended test for all individuals over the age of two. The fluid is protein from dead TB bacteria you cannot catch the disease from this test. People at lower risk for having TB need to have a larger bump to be diagnosed with a TB infection. If you are at higher risk, a smaller bump is considered a sign of infection. Results of the test depend on your risk for TB. Your doctor will consider your chance of having TB when looking at the skin test site. The size of the firm bump (not the red area) is measured 2 to 3 days after the test to find out the result. A firm red bump may mean you have been infected with TB bacteria at some time. If the test is done incorrectly, a false negative might occur. More tests-such as a chest X-ray, a sputum culture, or both-are usually done to see if you have an active TB infection.Redness alone at the skin test site usually means you haven't been infected with TB bacteria. People with recent TB infections and very old TB infections can also show false negative test results. It also can't tell the difference between a TB infection and a TB vaccination ( BCG vaccination). No firm bump forms at the test site, or a bump forms that is smaller than 5 mm (0.2 in.)Ī firm bump that is 5 mm (0.2 in.) or larger in size suggests a TB infection.Ī positive reaction can usually be seen for about 1 week.Ī positive tuberculin skin test doesn't mean you have contagious (active) TB. ![]() Only 10 individuals with initially positive results remained positive when the test was repeated the next year, and 9 of these 10 were QuantiFERON-TBnegative within 3 years. This protocol reduces the likelihood of a boosted reaction to subsequent TB skin tests in patients with no previous history of TB. Measurements vary for children, HIV victims and other high-risk groups. In the two-step protocol, a negative result after 48 to 72 hours requires a repeat test within 1 to 4 weeks. If the test turns out negative, you will experience a very small swelling or none at all. If you are at higher risk, a smaller bump is considered a sign of infection. QuantiFERON-TB results were positive in 80 of 557 tuberculin testnegative individuals examined annually for a maximum of 7 years. When you get a negative reaction after the test, it means that you haven’t been infected by the TB-causing bacteria at any point in your life. ![]() The size of the firm bump (not the red area) is measured 2 to 3 days after the test to find out the result. Negative TB blood test: This means that the persons blood did not react to the test and that latent TB infection or TB disease is not likely. A Tb Mantoux test results may sometimes be negative, but that does not always mean that a person is free of tuberculosis. Redness alone at the skin test site usually means you haven't been infected with TB bacteria. ![]()
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