Measurement of a Tuberculin Skin Test Reaction

Two to three days after getting a tuberculin skin test, the size of any bump at the site is measured. Your risk of having TB is used along with the size of the bump to determine whether the test is:

• Positive, meaning you have been infected with TB bacteria.
• Negative, meaning you have not been infected with TB bacteria or your body cannot respond to the protein injected because of a weakened immune system.

The test cannot tell if you have a latent (inactive) infection or active TB that can be spread to others.