Elicitation threshold of cobalt chloride: analysis of patch test dose-response studies

Background. Cobalt is a strong skin sensitizer (grade 5 of 5 in the guinea-pig maximization test) that is used in various industrial and consumer applications. To prevent sensitization to cobalt and elicitation of allergic cobalt dermatitis, information about the elicitation threshold level of cobalt is important. Objective. To identify the dermatitis elicitation threshold levels in cobalt-allergic individuals. Materials and methods. Published patch test dose-response studies were reviewed to determine the elicitation dose (ED) levels in dermatitis patients with a previous positive patch test reaction to cobalt. A logistic dose-response model was applied to data collected from the published literature to estimate ED values. The 95% confidence interval (CI) for the ratio of mean doses that can elicit a reaction in 10% (ED10) of a population was calculated with Fieller's method. Results. On the basis of five included studies, the ED10 values of aqueous cobalt chloride ranged between 0.0663 and 1.95 mu g cobalt/cm(2), corresponding to 30.8-259 ppm. Conclusions. Our analysis provides an overview of the doses of cobalt that are required to elicit allergic cobalt contact dermatitis in sensitized individuals, and thereby the basis for future prevention of cobalt allergy.