High frequency of contact allergy to gold sodium thiosulfate. An indication of gold allergy?

When gold sodium thiosulfate was added to the patch test standard series, positive reactions were obtained in 8.6% of 823 consecutive patients with suspect contact allergy. The test reactions were clinically of an allergic type and, in several cases, long-lasting. There was no correlation with other allergens in the standard series. In a special study on 38 patients with contact allergy to gold sodium thiosulfate, the following principal findings were obtained: positive patch tests to the compound itself in dilute concentration; positive patch tests to potassium dicyanoaurate; negative patch tests to gold sodium thiomalate, sodium thiosulfate, and metallic gold; positive intradermal tests to gold sodium thiosulfate. Our findings make gold sodium thiosulfate the 2nd most common contact allergen after nickel sulfate. It is suggested that a positive skin test to gold sodium thiosulfate represents gold allergy.