Comparison Testing of Current (PPD-S1) and Proposed (PPD-S2) Reference Tuberculin Standards

Abstract
Among low-risk subjects, the tests had equally high specificities (PPD-S1, 98.7% and PPD-S2, 98.5%), using a 10-mm cutoff. The number of discordant (negative versus positive) interpretations for PPD-S2, assuming that low-risk subjects who had a > 10 mm reaction to PPD-S1 were truly infected, was low (0.5%) and indis- tinguishable from the rate of discordant interpretations of the same test when read by two different observers (0.8%). The study results indicate that PPD-S2 is qualified to be used as the new U.S. reference standard for PPD tuberculin.