Tuberculosis skin, also known as PPD, testing may be performed to determine whether your body has developed an immune response to the bacteria that causes tuberculosis, either due to an ongoing infection, a past infection, or having received the BCG vaccination (which is not used in the U.S.) You may want to know your TB test status if you believe you may have been exposed to persons infected with TB, you work in healthcare, or you have traveled abroad in countries where risk of exposure is elevated. A small injection is made just under the skin of the forearm. You will then return in 48-72 hours to have a healthcare worker read the results of the test. A positive test is indicated by an area of localized thickening/hardening of the skin around the injection. In the event of a positive test, a doctor will help you decide what additional work-up and treatment may be necessary.