Tuberculin tine test
The tuberculin tine test is used to determine whether someone has been exposed to Tuberculosis.
How the test is performed
In this test, the tuberculosis antigen is injected just under the skin with a multi-pronged instrument. The antigen is located on the tines (spikes) that penetrate the skin. The site, most often on the arm, is usually labeled with ink so that it may be monitored.
After 48 to 72 hours, if the result is positive, the skin will appear red and swollen like a mosquito bite where the antigen was injected. A negative test result may be a bit red but will not be swollen and firm like a mosquito bite.
Note: The tuberculin skin test is more accurate than the tine test and 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
When the antigen is injected, there is a slight stinging sensation where the tines are inserted. After the reaction begins, the area may itch or burn.
Why the test is performed
This test is helpful in determining whether you have ever been exposed to Tuberculosis. If you have been exposed to tuberculosis at any time in the past, antibodies are formed by your body and remain in your system; when the tuberculosis antigen is injected under the skin during the tine test, your body will have an immune response, and there will be an area of inflammation at the site of the injection.
No inflammation will appear after the injection if you have never been exposed to tuberculosis.
What abnormal results mean
An inflammation zone indicates the immune system recognizes the antigen, and your body has been exposed to the bacteria that cause tuberculosis at some point in your life. A positive TB tine test does not mean that you have active tuberculosis, only that your body has been exposed at some point. 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.
A chest x-ray may be taken to evaluate whether you have active tuberculosis.
What the risks are
A very small amount of the antigen is injected, so the risks are minimal. Typical reactions include itching and hives. Sometimes, the area may blister. Rarely, the swelling may become very large.
Inform your health care provider if you experience any severe reactions.
The test may be falsely negative in the elderly and in patients with weakened immune systems, such as the following:
- AIDS patients
- Cancer patients who are undergoing Chemotherapy
- Organ transplant recipients
- Anyone taking high doses of steroids
by Dave R. Roger, M.D.