North American Contact Dermatitis Group Patch Test Results: 2017-2018

Background: Patch testing is an important diagnostic tool for assessment of allergic contact dermatitis (ACD). Objective: This study documented the North American Contact Dermatitis Group (NACDG) patch testing results from March 1, 2017, to December 31, 2018. Methods: At 14 centers in North America, patients with dermatitis were tested in a standardized manner with a screening series of 70 allergens and supplemental allergens as clinically indicated. Data were manually verified and entered into a central database. Descriptive statistics were estimated, and trends were analyzed using chi(2) test. Results: Overall, 4947 patients were tested. There were 3235 patients (65.4%) who had at least 1 positive reaction and 2495 patients (50.4%) had a primary diagnosis of ACD. Five hundred eighty-one patients (11.7%) had occupationally related dermatitis. There were 10,122 positive patch test reactions. Nickel remained the most commonly detected allergen (16.2%), followed by methylisothiazolinone 0.2% aqueous (15.3%) and methylchloroisothiazolinone/methylisothiazolinone 0.02% aqueous (200 ppm, 11.0%). Compared with the previous reporting periods (2015-2016 and 2007-2016), the proportion of positive reactions for the top 20 screening allergens statistically increased for only 1 allergen, propolis (3.4%; risk ratios = 2.05 [confidence interval = 1.66-2.54] and 1.82 [confidence interval = 1.57-2.11]). Four newly added allergen preparations, hydroperoxides of linalool (8.9%), benzisothiazolinone (7.3%), sodium metabisulfite (2.7%), and hydroperoxides of limonene (2.6%), all had a prevalence of greater than 2%. Approximately 1 (19.7%) in 5 tested patients had 1 or more clinically relevant reactions to an allergen not on the NACDG screening series; 13.2% of these were occupationally related. T.R.U.E. TEST (SmartPractice Denmark, Hillerod, Denmark) would have hypotheticallymissed 30% to 40% of reactions detected by the NACDG screening series. Conclusions: These results demonstrate the importance of a regularly updated screening allergen series. Methylisothiazolinone continues to be a significant allergen in North America. Patch testing with allergens beyond a screening tray is necessary for complete evaluation of occupational and non-occupational ACD.