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#Positive and negative tb test skin

Some people infected with the bacteria that cause TB may not have any reaction to the test. 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. Many people born outside of the United States have had the BCG vaccine, but it’s not given in the United States due to its questionable effectiveness. Some countries outside the United States that have a high prevalence of TB give the BCG vaccine. People who received a bacillus Calmette-Guérin (BCG) vaccine against TB may have a false-positive reaction to the PPD test. False-positive and false-negative results live in certain group settings, such as prisons, nursing homes, and homeless sheltersįor people without a known risk factor for TB, a 15 mm or larger firm swelling at the injection site indicates a positive reaction.are infants, children, or adolescents who’ve been exposed to high-risk adults.are immigrants who’ve come from a country that’s had a high TB rate in the past five years.have diabetes, kidney failure, or other conditions that increase their TB risk.

#Positive and negative tb test skin

have had a negative PPD skin test in the past two years.

Larger reactions (10 mm of swelling or more) are a positive result in people who: More tests are necessary to confirm the diagnosis. Members of these high-risk groups may require treatment, but a positive result doesn’t always mean that they have active TB.

have changes on a chest X-ray that appear to be the result of a previous TB infection.

This is a type of tuberculin skin test where tuberculin is injected intradermally.

have been in close contact with someone who has active TB The results of specialist screening tests to identify latent tuberculosis (TB) infection should be interpreted taking into account the persons immune status, history of exposure to TB and the Bacillus Calmette-Guérin (BCG) vaccination, and other risk factors.

The amount of swelling may be different for children, people with HIV, the elderly, and others at high risk.Ī 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: A negative result means that you most likely haven’t been infected with the bacteria that cause TB.

If the area of skin where you received the PPD injection isn’t swollen or is only slightly swollen 48 to 72 hours after the injection, the test results are negative.