Why Is Two-Step Testing Recommended?
Persons who have been infected with TB for many years may lose the ability to mount a positive reaction to tuberculin skin testing. However, a skin test will cause them to have positive reactions to subsequent tests, thus creating the possibility that the reader of the second test will identify the test subject as newly infected. To avoid that confusion, especially for individuals who are to be tested periodically, such as certain AOD employees, programs should employ a two-step testing procedure the first time they screen an individual for TB. Two-step testing calls for the administration of two tuberculin skin tests 1 to 3 weeks apart. If the first test is positive, the person is considered infected. If the first test is negative, a second test will be performed 1 to 3 weeks later. If the second test is positive, the person is probably infected; if it is negative, the person is probably not infected.
