Patch testing with nickel chloride in a hydrogel.

Various concentrations of NiCl2 in a hydrogel were evaluated as a possible alternative to the standard patch test material of 5% NiSO4 pet. Patch test responses were recorded on a total of 430 patients with known or suspected contact allergy. A NiCl2 concentration of 1% or less in the hydrogel failed to elicit a response in some patients who reacted to 5% NiSO4 pet. The 2% NiCl2 hydrogel produced a small increase in response frequency and may reduce false-negative reactions. Along with the ability of the material to improve the topical bioavailability of nickel ions, more irritant reactions were observed. However, in cases with a positive history and a negative patch test with petrolatum, the hydrogel prepared from Methocel-E-4M seems to be a useful alternative vehicle for water-soluble allergens.