The tuberculin tine test is used to determine whether someone has come in contact with the bacteria that causes tuberculosis.

This test uses a tiny spiked instrument to inject a small amount of the tuberculosis antigen just under your skin. This is most commonly done on the arm. Usually, the area is marked with an ink pen, so it can be checked for any redness and swelling at a later time, usually in 2 to 3 days.

Note: Another test, called the tuberculin skin test, is a more accurate than the TB tine test covered in this article, and is the preferred method of determining exposure to tuberculosis.

There is no special preparation. People with dermatitis or other skin irritations on their arms may need to have the test performed at a different spot on the body.

Some people feel a slight stinging sensation when the instrument is inserted under the skin. After the test, the area may itch or burn.

This test helps determine if you have ever been exposed to tuberculosis. If you have ever been exposed to tuberculosis, your immune system produced antibodies to help fight the disease. These remain in your body. When this test is performed, those with antibodies to tuberculosis will have a positive test result.

If you have a negative test result, the area may be a little red, but will not be swollen and firm like a mosquito bite. This means you have not been exposed to the bacteria that causes tuberculosis.

If you have been exposed to tuberculosis, the area will become red and swell like a mosquito bit in 48 to 72 hours. This is considered a positive test result. It means your body's immune system detected the substance injected under your skin. A positive TB tine test does not mean that you have active tuberculosis, only that you have been exposed at some point in the past.

A chest x-ray may be taken to evaluate whether you have active tuberculosis.

Once you have been exposed, all future TB tine tests will be positive. If you have a positive TB tine test, the Centers for Disease Control and Prevention (CDC) recommends that you have a TB skin test, unless the first tine test had a blistering or very large reaction.

The risk of severe side effects is very low. Typical reactions include itching and hives. Sometimes, the area may blister. Rarely, the area of swelling may become very large.

Tell your health care provider if you have any severe reactions.

The test results may be incorrect (false negative). False negative means the test suggests you haven't been exposed to tuberculosis, but you really have been.

This is more likely in the elderly and in patients with weakened immune systems, such as:

• AIDS patients
• Cancer patients who receive chemotherapy
• Those who receive organ transplants
• Anyone taking high doses of steroids