Interference of the positioning of nickel, chromium and cobalt in the results of patch tests.

Background: The positioning of substances, which are co-sensitizers and/or with a tendency to cross-react, is not considered in the technique when applying patch tests (PT).

Objective: To investigate the interference of the positioning of nickel (Ni), chromium (Cr) and cobalt (Co) in patch tests (PT) results, when applied close or distant from each other.

Methods: PT were performed in patients suspected of allergic contact dermatitis (ACD), using the standard battery (SB), with substances showing a tendency towards cross-react and co-sensitizers applied far apart, and an additional battery (AB) with the metals placed close to each other. For tabulation purposes, only the 96-h reading was considered.

Results: Of the 86 tested patients, 33 (38%) had negative testing for metals and 53 (62%) had one or more positive (+) tests for Ni, Cr and/or Co. Concordant results in both tests (SB/ AB) occurred in 18/53 (34%) and 35/53 (66%) had discordant results. Regarding the SB, of the 159 tests with metals (53 patients, three metals), 57 tests were (+) and 102 (-). In the AB, 87 tests were (+) and 72 (-), a statistically significant difference (p < 0.05). Of the 57 (+) tests in the SB, 35 were for Ni, 18 for Co and four for Cr. In AB the number of (+) tests was 87, with 45 (+) tests for Ni, 35 for Co and seven for Cr. The difference in the number of positive tests between the two batteries was statistically significant for Co and Ni.

Study limitations: The number of cases.

Conclusion: The results showed that the positioning of the metals interferes with the PT results and should be considered as part of the PT application technique.