Pilot evaluation of a convenient and cost-effective method of patch testing

Objective: The primary objective of this double-blind randomized, pilot study was to evaluate whether previously prepared stored patches may be as effective as freshly prepared patches are for detecting contact allergy. Methods: Two sets of 62 nonaqueous allergens were applied to participants' upper backs. One set was freshly prepared, and the second set was previously prepared and stored for an average of 6 weeks. Right or left back location for each set was randomly assigned. The primary outcome assessment compared the proportions of fresh and strong reactions in pairs with complete discordance (negative on one side and 1+, 2+, or 3+ on the other side). Results: In 71 patients enrolled, there were 169 positive reactions. Concordance (any combination of a 1+, 2+, or 3+ reaction on both sides) was found in 63% of pairs (95% Cl: 55.4, 70.0). Of the 25 pairs with complete discordance, there was no statistically significant difference between the rate of positive reactions for fresh and stored patches. Conclusion: Pilot evidence suggests that stored patches may be effective in detecting the majority of allergic contact reactions. Larger studies are needed to evaluate antigen-specific effects as well as effects of varying lengths of antigen storage.