Open, closed and intradermal testing in nickel allergy.

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.