A Patch Testing Initiative for the Investigation of Allergic Contact Dermatitis in a UK Allergy Practice: A Retrospective Study

Abstract

Patch testing is the gold standard diagnostic tool for investigating allergic contact dermatitis (ACD). In the United Kingdom, patch testing has been historically confined to the dermatologist's office. Furthermore, detailed studies on patch testing by allergists are significantly underrepresented at the international level. The objective of this study was to undertake a comprehensive evaluation of a patch testing initiative from an allergy practice; we report on various patient characteristics, prevalence and relevance data, in addition to immediate hypersensitivity testing. We undertook a retrospective analysis of 156 patients suspected of having contact dermatitis seen in our UK allergy practice between October 2016 and April2018. Of the 156 patients patch tested (mean age 36.9 years, female 88%, white ethnicity 71.8%, atopy 68.6%), ACD was diagnosed overall in 49% of the cohort and ACD of current relevance was assigned to 31%. Our extended British standard series alone detected the responsible allergen in 87% of patients, and the remaining 13% were detected from supplementary or own material testing alone. Most prevalent contact allergens were nickel (28.2%), p-phenylenediamine (8.3%), cobalt (8.3%), methylisothiazolinone (5.8%), and hydroperoxides of linalool (4.5%) and limonene (4.5%). A history of occupationally related dermatitis (P= .004) and initial (pretest) diagnosis of ACD (P<.001) were both significantly associated with relevant positive patch test reactions (atopy status was not associated P>.05). ACD was detected in almost 50% of assessed patients, and we highlight the importance of assessing relevance. Hydroperoxides of limonene and linalool are notable additions to the prevalence data. Patch testing should be incorporated into more allergy practices, although availability of training is a limiting factor.