Comparable specificity of 2 commercial tuberculin reagents in persons at low risk for tuberculous infection

Context One or both commercial tuberculin skin test reagents (Aplisol and T ubersol) may have a high rate of false-positive reactions. Objective To compare the reaction size and specificity of skin testing with Aplisol, Tubersol, and the standard purified protein derivative (PPD-S1), Design Double-blind trial, conducted between May 14, 1997, and October 28, 1997, in which each individual received 4 tuberculin skin reagents at sites assigned at random. Setting Health departments and universities in 6 US cities. Participants A total of 1555 persons at low risk of latent tuberculosis inf ection. Intervention Simultaneous skin tests with Aplisol, Tubersol, PPD-S1, and ei ther a second PPD-S1 or PPD-S2 (a proposed new standard). Main Outcome Measure Reaction size at each injection site measured by 2 inv estigators blinded to type of reagent. Results Aplisol produced slightly larger reactions than Tubersol, but this difference did not significantly change skin test interpretation. The mean +/- SD reaction sizes were 3.4 +/- 4.2 mm with Aplisol, 2.1 +/- 3.2 mm with Tubersol, and 2.5 +/- 3.6 mm with PPD-S1. Assuming that all participants w ere uninfected and using a 10-mm cutoff, the specificities of the tests wer e high: Aplisol, 98.2%; Tubersol, 99.2%; and PPD-S1, 98.9%, Significant var iability was not detected in interobserver, host, and lot-to-lot reagent co mparisons. Conclusion Using a cutoff of at least 10 mm, testing with 3 different PPD r eagents resulted in similar numbers of uninfected persons being correctly c lassified.