What is a two-step TB test?
A two-step tuberculosis test involves a person getting re-tested one week after the initial tuberculosis test. Use two-step testing for initial skin testing of adults who will be retested periodically (e.g., health care workers). This ensures that any future positive tests can be interpreted as being caused by a new infection, rather than simply a reaction to an old infection. Some people who were previously infected with TB may have a negative reaction when tested years after infection due to the immune system response gradually lessening with time.
