Copper allergy revisited.

Abstract

Positive patch tests to copper sulfate are regularly observed, although copper is reported as a rare allergen with a low sensitizing potential. Usually they are claimed to be irritant and unspecific. The aim of this study was to assess the relevance and the diagnostic value of positive reactions to copper. A total of 2660 routine patch tests were analyzed for positive reactions to copper and other metal allergens: copper, 3.53%; nickel, 21.02%; palladium, 5.90%; cobalt, 3.31%. Reactions to copper and nickel were highly significantly associated with each other. Twenty-six patients with a positive routine test to copper were retested. The reproducibility was modest (38%), but again significantly associated with nickel sensitization. These clinical data support a copper-nickel cross-reactivity concept on T-cell level based on recently published molecular data. We conclude that positive patch tests to copper are mostly specific; however, they are usually of low clinical relevance.