Quantification and specificity of the repeated open application test (ROAT). A methodological study using cobalt and colophony in guinea pigs.

The repeated open application test is used to assess the clinical relevance of positive patch test reactions to ingredients of formulated products. The great variation in outcome is usually claimed to be related to the concentration of the allergen responsible. We have here studied the quantitative aspects, specificity and effect of patch testing on the outcome of the repeated open application test in an animal model, using guinea pigs sensitized with cobalt chloride or colophony. Thresholds of sensitivity were determined before and after the topical treatments. Clear dose-response relationships were established. The reactivity in sham-treated controls and to the vehicles was minimal. The concordance between patch test results and outcome of the use tests was concentration-dependent and at low concentrations < 50%. The repeated open application test is a useful method, but some of the basic issues need further evaluation. This animal model will hopefully serve this purpose.