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What is tuberculin skin test?

A tuberculin skin test is a medical test to determine if someone has been infected with the bacteria that cause tuberculosis, Mycobacterium tuberculosis. A tuberculosis infection affects the lungs, causing a long-lasting bad cough that might include coughing up blood and/or mucus, as well as a fever, loss of appetite and weight, weakness and fatigue and other symptoms. If left untreated, tuberculosis can be deadly.

The tuberculin skin test, also known as a PPD skin test, requires two office visits to your doctor. In the first visit, your doctor will inject a small amount of a harmless liquid that contains purified protein derivative or PPD under the skin of your arm, using a very small gauge needle. Your doctor will ask you to return to the office in two to three days. During this second visit, your doctor will examine your arm to see how you reacted to the injection. If there is no change in your arm area, or only mild swelling, the test is negative; it is very unlikely that you have tuberculosis.

If you have a round, swollen, red lesion at the site of the injection, your doctor will measure it. If the lesion is 15 mm in diameter or greater, you have tested positive for tuberculosis. A measurement of 5 mm can also be determined to be positive in certain people who have serious conditions that weaken their immune system; a measurement of 10 mm is positive in young children, health care workers, or certain other subsets of the population. A measurement of 15 mm is positive in anyone.

A tuberculin skin test is not recommended as a screening test for the general population but may be recommended in certain people including:
  • people who show signs of a possible tuberculosis infection
  • people from out of the country who come from an area where tuberculosis is prevalent
  • health care workers
  • anyone who has been in close contact with someone who has tuberculosis
  • people with compromised, weak immune systems (such as someone who has HIV/AIDS)
  • people who inject illicit drugs

Continue Learning about Tuberculin

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.