When PPD testing of adults is to be repeated periodically (as in HCW skin testing programs), two-step testing can be used to reduce the likelihood that a boosted reaction is misinterpreted as a new infection. Two-step testing should be performed on all newly employed HCW's who have an initial negative PPD test result at the time of employment and have not had a documented negative PPD test result during the 12 months preceding the initial test. A second test should be performed 1-3 weeks after the first test. If the second test result is positive, this is most likely a boosted reaction, and the HCW should be classified as previously infected. If the second test result remains negative, the HCW is classified as uninfected, and a positive reaction to a subsequent test is likely to represent a new infection with M. tuberculosis.
Boosting "Waned" Hypersensitivity
- 1st PPD not significant -- but provides stimulus to increase size reaction on 2nd test
- Differentiates between "waned hypersensitivity and recent infection
- Influences whether INH preventive therapy is started