Respiratory Diseases

Allergic Reactions to TB Test

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Tuberculin skin tests are used to determine if you have ever been exposed to tuberculosis (TB). Typically, these tests are given as a means to screen people who will be living or working with populations at risk of being exposed to TB. They are also given to people who may have already been exposed to TB or for those who have been prescribed certain medications. The Mantoux tuberculin skin test is currently the standard way to determine if a person has been infected with Mycobacterium tuberculosis.

The Mantoux test is done by injecting a small amount of TB antigens under the top skin layer on your forearm. If the test is positive, your skin will react to the antigens with a couple of days by developing a red bump. If the test is negative, there will be no reaction. Sounds simple, right? It is simple, except for the fact that some people are allergic to tuberculin skin tests.

Your immune system is specially designed to protect your body from harmful invaders like germs and toxins. You will experience an allergic reaction if your body mistakenly identies a harmless substance as something toxic. Substances that cause allergic reactions are called allergens. Your body's reaction to an allergen can run the gamut, from a simple skin rash to anaphylaxis, which can be life threatening. Anything can be an allergen, even a skin test for tuberculosis.

Being allergic to tuberculin skin tests can present special problems, since your health care provider will be specifically looking for a skin reaction after a typical TB test. A rash after a TB test generally indicates a positive result, but it may also be the result of an allergic reaction to the TB antigens. If you develop a skin reaction after a TB test, your health care provider may order other tests to determine if you have ever been infected with Mycobacterium tuberculosis. It is likely that your health care provider will have you get a chest x-ray and undergo blood tests. If the other tests are negative, chances are good that you are allergic to TB antigens.

If it turns out you are allergic to tuberculin skin tests, it's important to let all of your future health care providers know. Allergic reactions to allergens tend to become more severe after repeated exposures. Your health care provider may be able to use a new type of TB test to determine whether or not you have been exposed to the organisms that cause tuberculosis. The new test is not yet widely available, but it only requires one office visit and isn't affected by previous vaccinations.

On the Web: "New single-visit TB test first in Valley"

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