Comparison of Nickel Sulfate 2.5% and Nickel Sulfate 5% for Detecting Nickel Contact Allergy

Nickel is among the most common contact allergens found on patch testing worldwide and, because of its ubiquitous nature in our environment, often has important implications for allergen avoidance strategies. In both North America and Europe, nickel positivity is found in approximately 20% of patients who undergo patch testing. Whereas in North America, nickel sulfate is typically tested at a concentration of 2.5%, in Europe, it is tested at a 5% concentration.

The primary objective was to assess the differences in patch test positivity to nickel sulfate 2.5% and 5%.

We investigated 205 consecutive patients between September 2017 and February 2018 who were tested to nickel sulfate at concentrations of both 2.5% and 5%.

Among the 205 patients tested, 33% were positive (+, ++, or +++) to at least 1 concentration of nickel sulfate, 20% were positive to nickel sulfate 2.5%, and 31% were positive to nickel sulfate 5% (χ1(N = 205) = 16.1, P = 0.0001). Patients were 6.5 times more likely to have a positive reaction to nickel sulfate 5% than 2.5% (odds ratio 95% confidence interval, 2.3-25.6).

Given our findings, we propose an additional evaluation of nickel sulfate 5% as a standard allergen for patch testing in North America.