Skip to content
    Font Size
    A
    A
    A

    Tuberculin Skin Test

    Results continued...

    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. People at low risk for having TB need to have a larger bump to be diagnosed with a TB infection.

    Three levels of risk have been defined:

    • High-risk group includes people who have HIV, those who have had close recent contact with a person who has an active TB infection, and those who have symptoms or a chest X-ray that shows TB. Other people at high risk for tuberculosis include those who take medicines that contain corticosteroids for a long time or people taking biologics (used to treat rheumatoid arthritis and Crohn's disease).
    • Moderate-risk group includes people who have recently moved from or traveled in a country with a high rate of TB; those who use illegal drugs by injection (intravenous drug users); people who live in nursing homes; workers in hospitals, nursing homes, schools, and prisons; children younger than 4 years old; children (ages 4 to 18) who are exposed to high-risk adults; and homeless people. Others at moderate risk for having tuberculosis include people who are 10% or more below their ideal body weight and people who have kidney failure, diabetes, leukemia, cancer, or those who have had part of their stomach removed (gastrectomy).
    • Low-risk group includes people who do not have any possible exposure to TB listed in the other risk groups.

    A positive reaction usually remains visible for about 1 week.

    Mantoux tuberculin skin test
    Normal (negative results):

    No firm bump forms at the test site, or a bump forms that is smaller than 5 mm (0.2 in.).

    Abnormal (positive results):

    A firm bump that is 5 mm (0.2 in.) in size suggests a TB infection in people who are in a high-risk group.

    A firm bump that is 10 mm (0.4 in.) in size suggests a TB infection in people who are in a moderate-risk group.

    A firm bump that is 15 mm (0.6 in.) in size suggests a TB infection in people who are in a low-risk group.

    A positive tuberculin skin test does not mean you have a contagious (active) infection. The test cannot tell if the infection is active or inactive (latent TB). It also cannot tell the difference between a TB infection and a TB vaccination (BCG vaccination). 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.

    WebMD Medical Reference from Healthwise

    Last Updated: August 26, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

    Hot Topics

    WebMD Video: Now Playing

    Click here to wach video: Dirty Truth About Hand Washing

    Which sex is the worst about washing up? Why is it so important? We’ve got the dirty truth on how and when to wash your hands.

    Click here to watch video: Dirty Truth About Hand Washing

    Popular Slideshows & Tools on WebMD

    disciplining a boy
    Types, symptoms, causes.
    fruit drinks
    Eat these to think better.
    embarrassed woman
    Do you feel guilty after eating?
    diabetes supply kit
    Pack and prepare.
    Balding man in mirror
    Treatments & solutions.
    birth control pills
    Which kind is right for you?
    Remember your finger
    Are you getting more forgetful?
    sticky notes on face
    10 tips to clear your brain fog.
    Close up of eye
    12 reasons you're distracted.
    woman biting a big ice cube
    Habits that wreck your teeth.
    apple slices with peanut butter
    What goes best with workouts?
    Pink badge on woman chest to support breat cancer
    Myths and facts.

    Pollen counts, treatment tips, and more.

    It's nothing to sneeze at.

    Loading ...

    Sending your email...

    This feature is temporarily unavailable. Please try again later.

    Thanks!

    Now check your email account on your mobile phone to download your new app.

    Women's Health Newsletter

    Find out what women really need.