Reproducibility of patch tests: comparison of identical test allergens from different commercial sources

The reproducibility of patch tests is an important determinant of the clinical value of this diagnostic procedure. The aim of the present study was to delineate comparatively the efficiency and reproducibility of identical test reagents from 2 different commercial sources. Purchased in duplicate from brial and Boots-Hermal, 30 allergens from the European standard and an extension series were simultaneously applied to Finn Chambers and affixed next to each other. Out of 2070 paired patch tests in 71 patients, 97.2% presented with concordant-negative results. 60 patch tests were classified as allergic with 95% concordant-positive results. From these paired positive patches, a subgroup of 13 (22.8%) corresponding allergens presented with minor differences in the visible strength of the allergic reaction. Generated by cobalt chloride, formaldehyde and 2-bromo-2-nitropropane-1,3-diol in 1 patient each, discordant results, i.e. 1 positive and 1 negative test in parallel, were found in only 5%. Taken together, we were able to demonstrate that patch test preparations from 2 different companies exhibited a high level of reproducibility. This standardized quality of test reagents from different suppliers provides useful information on several aspects of everyday practice.