Patch testing is an important diagnostic tool for the assessment of allergic contact dermatitis (ACD).
This study documents the North American Contact Dermatitis Group (NACDG) patch testing results from January 1, 2015, to February 28, 2017.
At 13 centers in North America, patients were tested in a standardized manner with a screening series of 70 allergens. Data were manually verified and entered into a central database. Descriptive frequencies were calculated, and trends were analyzed using χ2 test.
A total of 5597 patients were tested. There were 3725 patients (66.6%) who had at least 1 positive reaction, and 2798 patients (50.2%) were ultimately determined to have a primary diagnosis of ACD. A total of 572 patients (10.2%) had occupationally related skin disease. There were 10,983 positive allergic reactions. Nickel remained the most commonly detected allergen (17.5%). Methylisothiazolinone, which was added to the screening series for the 2013–2014 cycle, had the second highest positive reaction rate of allergens tested (13.4%). Compared with the previous reporting periods (2013–2014) and (2005–2014), positive reaction rates for the top 35 screening allergens statistically increased for only 1 allergen: hydroxyethyl methacrylate (3.4%; risk ratios, 1.24 [confidence interval, 1.00–1.54] and 1.46 [confidence interval, 1.23–1.73]). Three newly added allergen preparations—ammonium persulfate (1.7%), chlorhexidine (0.8%), and hydroquinone (0.3%)—all had a reaction rate of less than 2%. Twenty-three percent of the tested patients had at least 1 relevant allergic reaction to an allergen not on the NACDG series; 12% of these were occupationally related. T.R.U.E. Test (SmartPractice Denmark, Hillerød, Denmark) would have hypothetically missed one quarter to almost 40% of reactions detected by the NACDG screening series.
These results confirm that the epidemic of sensitivity to methylisothiazolinone has continued in North America. Patch testing with allergens beyond a screening tray is necessary for a complete evaluation of occupational and nonoccupational ACD.