Open, closed and intradermal testing in nickel allergy

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Abstract
Open, closed and intradermal testing with NiCl2 was performed in 15 subjects with patch‐test‐proven allergy to 5% NiSO4 in pet. Intradermal testing proved to be a reliable method in confirming nickel sensitivity within 24 h. Open testing with non‐toxic concentrations of NiCl2 in alcohol resulted in 73% and 93% positive reactions at 24 h and 48 h readings, respectively. This test method can be used as a reliable screening method in nickel allergy. Open testing often resulted in positive reactions within a few hours. This makes it possible to investigate pathogenetic events of acquired allergic contact dermatitis at a much earlier stage than with the usual 48‐h occlusion. 24‐h occlusion with Finn Chambers is not sufficient if one is to avoid false negative reactions in nickel allergy. Occlusion with Finn Chambers seems to delay the reaction.