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For a TB skin test, a health care worker uses a small needle to put some testing material, called tuberculin, just under your skin. This is usually done on the lower inside part of your arm. After you get the test, you must return in 2 to 3 days to see if there is a reaction to the test. If there is a reaction, the size of the reaction is measured.
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Tuberculosis (TB) is a disease that usually affects the lungs. TB sometimes affects other parts of the body, such as the brain, the kidneys, or the spine. The TB disease can cause death if untreated.
TB germs are spread from person to person through the air. TB germs are put into the air when a person with TB disease of the lungs or throat coughs, sneezes, laughs, or sings. TB is not spread by sharing silverware or cups, sharing cigarettes, or sharing saliva when kissing someone.
People with the TB disease often feel weak or sick, lose weight, have fever, and have night sweats. If their TB disease is in the lungs, they may also cough and have chest pain, and they might cough up blood. Other symptoms depend on what part of the body is affected.
People with TB disease are sick from the large number of TB germs that are active in their body. They usually have one or more of the symptoms of TB disease. These people may pass TB germs to others. The TB disease can cause permanent body damage and death. Medicines which can cure TB disease are given to these people.
People with TB infection also have the germs that cause TB in their body. But they are not sick because there are not as many of the germs, and the germs lie dormant (sleeping) in their body. They cannot spread the germs to others. However, these people could develop TB disease in the future, especially if they are in one of the high-risk groups listed under "Who gets TB disease?" People with TB infection can take medicine to prevent them from developing TB disease.
Once a person has TB infection, he or she has a higher chance of getting TB disease if the person:
Get a TB skin test or the QuantiFERON®-TB Gold (QFT) blood test. If you have a positive reaction to either of the tests, you will probably be given other tests to see if you have TB infection or TB disease.
You can get a TB skin test from your doctor or local health department.
A negative skin test usually means you are not infected. However, the test may be falsely negative if you were infected recently. It usually takes 2 to 10 weeks after exposure to a person with TB disease for your skin test to react as positive. The test may also be falsely negative if your immune system is not working properly.
A negative QFT usually means you are not infected.
A positive skin test or QFT usually means that you have been infected with the TB germ. It does not necessarily mean that you have TB disease. Other tests, such as an x-ray or sputum sample, are needed to see if you have TB disease.
BCG is a vaccine for TB. This vaccine is not widely used in the United States, but it is often given to infants and small children in other countries where TB is common. The BCG vaccine does not usually protect adults against TB. You may still get TB infection or TB disease. Even if you have had the BCG vaccine, you will need a TB skin test or QFT to see if you may have TB infection or TB disease.
Get the required follow-up tests. Follow your doctor’s advice and take the medicine as prescribed. Today, both TB infection and TB disease can be treated and cured with medication.