REPEATED tuberculin tests in the same site.

When the tuberculin-testing technique for the Tuberculosis Research Office field studies became so standardized that successive tests were being placed in about the same site on the forearm, there was a sudden and pronounced increase in the frequency of bullous reactions.Preliminary trials pointed to repeated testing in the same site as the most likely cause of this altered response to tuberculin. To obtain further information, a study was carried out on 356 mental patients, each receiving an initial test with 5 TU in one forearm and 3 months later two follow-up tests with 5 TU-one in the same site as the initial test and one in the corresponding site on the other forearm.This study shows that among tuberculin-sensitive persons the response to tuberculin injected into the site of a previous test differs both in size and in character from the response to tuberculin injected into an unused site. In the previously used sites the tuberculin reactions appear sooner and fade sooner than reactions in new sites; they attain greater maximum size and present a much higher frequency of bullae. Thus, the "used-site" phenomenon may cause practical problems in the interpretation of reactions in programmes involving periodic tuberculin-testing.