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Tuberculin Skin Test


  • A tuberculin skin test is done to see if you are infected with the germ that causes tuberculosis (TB). Tuberculin is a liquid that caregivers inject into the skin of your arm. Your skin will react to tuberculin if you are infected. Tuberculosis is a serious infection that usually starts in the lungs. TB germs are easily spread from one person to another through the air. The germs can live in your body a long time without making you sick. This is called latent TB. Latent TB can develop into active TB if it is not treated.
  • A TB skin test may be done if you live or have spent time with someone who has TB. The test is often done if you have signs of active TB. For example, you cough up blood or have night sweats. You may need to be tested if you share needles to inject drugs. A TB test may also be needed as screening for a job or if your immune system is weak from disease.


After the test:

  • Return in 2 to 3 days: Your skin must be checked 2 to 3 days after the test. You will need another TB skin test if you do not come back within 3 days.
  • Watch for signs of allergic reaction: Some people have an allergic reaction to tuberculin. Seek help immediately if you have any symptoms of allergic reaction, such as hives or swelling.

What the test results mean:

The TB skin test can only show that you were infected with the germ that causes tuberculosis. You will need more tests to learn if you have latent or active TB. The most common tests are chest x-rays and sputum samples.

  • Positive test: Your test is positive if the area around the skin test is raised or hard. Your test can be positive even if you do not have active TB. This would happen if you received a BCG vaccination for TB.
  • Negative test: Your test is negative if there is no change to your skin. Your test can be negative even if you do have TB. Your immune system may be too weak to react to the tuberculin, or your infection may be too recent.

Contact your primary healthcare provider if:

  • You have questions or concerns about the test or about tuberculosis.

Return to the emergency department if:

  • You have chest pain.
  • You have a mild cough that gets worse. You may cough up white, yellow blood-streaked sputum.
  • You have blisters, ulcers, or your skin has turned black in the injection area.
  • Your skin is itchy, or you have a rash or hives that are spreading.
  • Your face is red and swollen.
  • Your mouth is swollen, your throat feels tight, or you have trouble breathing.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.