Evaluation of the Multi-Test device for immediate hypersensitivity skin testing.

Test-to-test reproducibility, user variability, and the effect of positive reactions on adjacent negative sites were evaluated for the Multi-Test skin testing device. Twenty-five subjects had skin tests with 24 histamine (1 mg/ml), four glycerosaline controls, and four "dry" controls on two testings 7 days apart. To assess reproducibility from large and smaller histamine reactions and/or their effect on adjacent negative controls, 10 of the 25 subjects were retested once with the same testing format, but histamine at 10 mg/ml was substituted. To determine whether large allergen reactions affect adjacent negative controls differently than histamine reactions, 24 additional patients were retested on arms and back with negative controls adjacent to allergens to which they had prior 3+ to 4+ skin test reactions. Conclusions from 2688 skin tests on 49 patients are as follows: large (mean > 10 mm) histamine reactions reproduced better than smaller (mean < 7 mm) responses--coefficients of variation were 12.3 and 21.4 respectively. A 14% user variability occurred when comparing mean wheal sizes from histamine produced by each nurse and 1.2% when comparing their coefficients of variation. Neither small histamine reactions nor large reactions from histamine and allergens affected adjacent negative controls. We conclude that Multi-Test is a highly reliable skin testing technique that provides good reproducibility of results and low user variability.