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TB Skin Test

The skin test for TB is the most common method of detecting latent tuberculosis. You should get a skin test if you think you might have active tuberculosis, have spent time with someone known to have active tuberculosis, or inject illegal drugs. During this test, a special fluid is injected into the forearm. A healthcare provider will measure the swelling after 72 hours and determine the results.

What Is the TB Skin Test?

There are two TB (tuberculosis) tests that can be used to detect latent cases of disease. The more common one is a TB skin test (also known as a PPD test). You can get this test at the health department or at your doctor's office.
 

Who Should Get a Skin Test for TB?

You should get a TB skin test if:
 
  • You have spent time with a person known to have active tuberculosis or suspected to have active tuberculosis
     
  • You have HIV infection or another condition that puts you at high risk for active tuberculosis
     
  • You think you might have active tuberculosis
     
  • You are from a country where active tuberculosis is common (most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia)
     
  • You live somewhere in the United States where active tuberculosis is more common, such as a homeless shelter, migrant farm camp, prison or jail, or some nursing homes)
     
  • You inject illegal drugs.
     

How Does the TB Skin Test Work?

With this test, a healthcare worker will inject a small amount of testing fluid (called tuberculin or PPD) just under the skin on the underside of the forearm. After two or three days, you must return to have your skin test read by the healthcare worker. You may have a swelling where the tuberculin was injected. The healthcare worker will measure this swelling and tell you if your reaction to the tuberculosis skin test is positive or negative (see TB Skin Test Reading). A positive reaction usually means that you have been infected by someone with active tuberculosis.
 

Tuberculosis Disease

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