Definition

The tuberculin tine test is used to determine whether someone has been infected with the bacteria that causes tuberculosis. However, the test is rarely used because other tests are more accurate.

Alternative Names

TB tine

How the test is performed

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 forearm. 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 - 3 days.

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

How to prepare for the test

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.

How the test will feel

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

Why the test is performed

This test helps determine if you have ever been exposed to, or infected with tuberculosis. If you have ever been infected with tuberculosis, your immune system produced substances called T-cells to help fight the disease. These T-cells stay in your body.

When this test is performed, the T-cells against tuberculosis will produce a positive test result.

Normal Values

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

What abnormal results mean

If you have been infected with tuberculosis, the area may become red and swell like a mosquito bite in 48 - 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. It only means that you have been exposed and infected at some point in the past.

A chest x-raymay be taken to determine whether you have active tuberculosis.

If you have a positive TB tine test, you should also have a TB skin test.

What the risks are

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.

Special considerations

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. Incorrect results are more common with this test than with the tuberculin skin test.

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

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

References

Friedland JS. Tuberculosis. In: Cohen J, Powderly WG, Berkley SF, et al, eds. Infectious Diseases. 2nd ed. Philadelphia, Pa: Mosby Elsevier; 2004:chap 37.

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