2013 Re: T.R.U.E Test and gold Dear Health Care Professional ...

It is well established that a contact allergic reaction to the gold salt, gold sodium thiosulfate (GST), is morecommon than allergic contact dermatitis to elemental gold or its alloys. So such a response is not surprising. Infact, these findings have generated considerable controversy about the clinical relevancy of gold as an allergen.As discussed in the previous questions, however, support for the clinical relevance of gold continues toincrease.Furthermore, sensitivity to gold as metal can be overlooked. Careful questioning of patients may yield clues thatsupport the presence of a gold allergy. The body sites most likely to be involved are fingers and earlobe.Provocation by an intramuscular injection of gold sodium thiomalate has even been associated with a flare up ofallergic contact dermatitis from a gold necklace previously worn around the neck. As with any allergen, manycomplicated factors are involved in interpreting patch test reactions to gold. Nonetheless, the American ContactDermatitis Society has noted that patch testing to gold may be particularly worthwhile in individuals withfacial/eyelid dermatitis and in those with long-term oral gold exposure.Is it normal for a high percentage of patients to test positive to gold?Yes. In a carefully conducted, blinded, dose-response clinical trial, about 35% of patients had mild to moderatepersistent reactions to gold sodium thiosulfate (GST) that included erythema and infiltration (most common),pruritus, and hyper- and hypopigmentation. In the literature rates of positive reactions to gold have ranged fromless than 10% to more than 70%. Consequently, it is reasonable to expect that many patients will have apositive response to patch testing with GST.However, not all reactions to GST may be clinically relevant. As with any allergen, the clinical relevance of areaction to gold for any given patient must be assessed by the clinician. Strategies for establishing clinicalrelevance include careful questioning of the patient to determine past and present reactions and exposures (i.e.,occupational and nonoccupational) to the allergen as well as further testing as deemed necessary.Is the concentration of gold in T.R.U.E./TRUE Test too strong?No. T.R.U.E./TRUE TEST is designed to optimize exposure of allergens to skin for reproducible and consistentresults with few irritant or false positive reactions. T.R.U.E./TRUE TEST is currently the only allergen patchtest approved by governmental authorities in both the United States and Europe. For example, to qualify forFDA approval in the United States, the dose of gold sodium thiosulfate (GST) used in T.R.U.E./TRUE Test hadto be determined in a carefully conducted, blinded, dose-response study of patients with a known sensitivity tothe allergen.These patients were patched tested for 48 hours to 6 different doses of GST. The doses were selected based onrecommendations from leading international dermatologists and on the concentrations used in othercommercially available preparations. These other commercial products use concentrations of 0.5 or 2.0%,which correspond to concentrations in T.R.U.E./TRUE Test of about 0.020 or 0.080 mg/cm 2 . Reactions wereread according to recommendations from the International Contact Dermatitis Group.The dose selected for use in T.R.U.E./TRUE test (75 mcg/cm 2 ) met the established criteria of being the lowestconcentration to elicit a +1 or +2 positive reaction in 70 to 90% of the sensitive subjects. Furthermore, theconcordance (percent agreement) between the T.R.U.E./TRUE Test allergen and the reference allergen insensitive patients was more than 84%, further supporting the appropriateness of the concentration.2