Jochen Brasch, Michael Weichenthal, Christiane Szliska, Harald Löffle, Patrick Koch, Jürgen Grabbe, Vera Mahler, Bo Kreilgård, Ulla Hoeck
DOI: 10.1080/00015555-0095

It is tacitly assumed that a positive patch test reaction is not affected by adjacent negative tests. However, despite its fundamental importance for the interpretation of test reactions this assumption has not been proven. To test this assumption, special TRUE-test® strips were prepared containing placebo, nickel sulphate and fragrance mix as the only allergens, separated by distances of 1 cm and 7 cm and blinded to the investigators. Patients were synchronously tested with two strips. Out of 493 patients tested in 6 centres, the 93 with positive reactions to nickel sulphate only were evaluated. No relevant difference was found between positive nickel reactions in the two different distances to a negative fragrance patch test. We conclude that a positive patch test reaction is not affected by adjacent negative patch tests, which therefore can be neglected for the interpretation of positive reactions.