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

One or both commercial tuberculin skin test reagents (Aplisol and Tubersol) may have a high rate of false-positive reactions.

To compare the reaction size and specificity of skin testing with Aplisol, Tubersol, and the standard purified protein derivative (PPD-S1).

Double-blind trial, conducted between May 14, 1997, and October28, 1997, in which each individual received 4 tuberculin skin reagents at sites assigned at random.

Health departments and universities in 6 US cities.

A total of 1555 persons at low risk of latent tuberculosis infection.

Simultaneous skin tests with Aplisol, Tubersol, PPD-S1, and either a second PPD-S1 or PPD-S2 (a proposed new standard).

Reaction size at each injection site measured by 2 investigators blinded to type of reagent.

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 were uninfected and using a 10-mm cutoff, the specificities of the tests were high: Aplisol, 98.2%; Tubersol, 99.2%; and PPD-S1, 98.9%. Significant variability was not detected in interobserver, host, and lot-to-lot reagent comparisons.

Using a cutoff of at least 10 mm, testing with 3 different PPD reagents resulted in similar numbers of uninfected persons being correctly classified.