Background: Allergic contact dermatitis is a significant cause of cutaneous disease for which patch testing often provides diagnostic support. Objective: This paper reports, as a follow-up of our previous studies, the results of patch testing from July 1, 1992, to June 30, 1994, by the North American Contact Dermatitis Group. Methods: Patients evaluated in the patch test clinics of the North American Contact Dermatitis Group were tested to the same screening tray of allergens using a standardized patch testing technique. The data from these patients were recorded on a standard computer entry form and analyzed. Results: Fifty-two allergens were tested during a 2-year period on 3,549 patients. Sixty-five percent of patients had positive patch test reactions. Fifty-two percent of the patients had reactions believed to be clinically relevant to the present or past dermatitis. The 20 standard screening allergens commercially available in the United States accounted for only 50% of the patients with positive allergic reactions. The 12 most frequent contact allergens were nickel sulfate, fragrance mix, thimerosal, quaternium-15, neomycin sulfate, formaldehyde, bacitracin, thiuram mix, balsam of Peru, cobalt chloride, p-phenylenediamine, and carba mix. The present and past relevance varied with the specific allergen from 45% (thimerosal) to 84% (thiuram mix). Among some newer allergens, methyldibromoglutaronitrile/phenoxyethanol (cosmetic preservative) caused positive reactions in 1.5% of the patients, and tixocortol-21-pivalate (corticosteroid) was positive in 2.5%. Conclusion: Patch testing remains a worthwhile diagnostic tool in the evaluation of patients with suspected allergic contact dermatitis. The usefulness of this technique is enhanced with the number of allergens tested. The information from this investigation will aid further development of a standard series for North America.
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