The 100-year history of the pach test in Hungary Importance of the 7th day assessment: confirmation of methodological recommendation in light of 15 years of data

Abstract

Patch test (PT) is the standard diagnostic tool verifying contact hypersensitivitiy (CH). Not only delayed but also immediate-type reactions can be detected. The methodology, and the tested allergens were formed as a result of continuous development and change in the 20th and 21st centuries to the present days. During PT, standard amount and concentrations of allergens are applied to the asymptomatic back of the patients. The provoked skin reactions are evaluated at specific intervals: the first reading is performed in 20-60. minutes, and after 48 hours of allergen exposure (occlusion), it occurs at 48, 72, 96 hours and on the 7th day. In Hungary, we have been using the PT for 100 years. The 7th day evaluation was recommended in 2008, and has been used by the Allergology Workgroup of our clinic since 2007. Many important allergens can give CH reactions only on the 7th day, so without this reading, a significant number of the reactions would not be detected. During our 15-year study period (2007-2021), in 624 patients out of 5790 tested population (10.7% of patients), and in 729 out of the total 3338 positive reactions (21.8% of reactions) were registered only on the 7th day in the environmental standard series. The most common allergen-groups were metals, mercury derivatives, preservatives, fragrances – plant components and drugs – local therapeutics. Regarding the individual allergen ranking, nickel (11.4%) was the most common. Among fragrances wood tar (3.7%), from preservatives Kathon CG® (4.0%), and among drugs – local therapeutics neomycin sulfate (5.2%) can be mentioned. Our data confirm and justify the methodological recommendation formulated in Hungary in 2008: the evaluation of the PT is necessary until the 7th day.