Patch testing is an important diagnostic tool for assessment of allergic contact dermatitis (ACD).
This study documented the North American Contact Dermatitis Group (NACDG) patch testing results from March 1, 2017, to December 31, 2018.
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 χ2 test.
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, Hillerød, Denmark) would have hypothetically missed 30% to 40% of reactions detected by the NACDG screening series.
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.