REPEATED TUBERCULIN TESTS AT SAME SITE IN TUBERCULIN-POSITIVE PATIENTS

Abstract

The tuberculin test with 1 TU was repeated three more times at monthly intervals in the same skin area in 100 tuberculin-positive patients. The readings were done at 3, 6, 12, 24, 48 and 72 hours, and on the fifth and seventh days. The average of the original tests showed the typical course of the delayed reaction, which reached the positive range at 12 hours, and its maximum at 48 hours, and remained in the positive range through 7 days. The average of the repeated tests showed the typical course of the combined reaction, which started within 3 hours, reached its maximum at 24 hours, attained a greater size, showed more frequent vesiculations, and disappeared earlier. The combined reaction is a dual one: the local sensitization reaction which is superimposed upon the usual delayed reaction. This study confirms the local sensitization effect of the tuberculin test in tuberculin-positive patients described in earlier studies. The practical significance of this phenomenon is that it may increase nonspecific reactions by cross-sensitization and lead to false positive readings with a single reading at 48 or 72 hours, and that the combined reaction of repeated tests in a sensitized area usually disappears earlier, which may lead to false negative readings.