Reproducibility and use of low-concentration skin prick test

We aimed to evaluate the reproducibility of the skin prick test performed w ith serial 1:4 dilutions of commercial standardized extracts in comparison with serum-specific IgE and the undiluted commercial extract. Twenty-four s ubjects sensitized to one (17 cases) or two (seven cases) inhalant allergen s were selected and submitted to duplicate skin prick tests with concentrat ed commercial allergenic extracts or with serial 1:4 dilutions of the same extracts in two different examinations 7 days apart. Blood samples were obt ained from 17 of the 24 patients for specific IgE determination. No statist ically significant within-patient variations in the area of the wheal in sk in prick tests done 1 week apart were found up to the eighth dilution (1:25 6) of the commercial allergen. On a patient-by-patient basis, only some dil utions showed a statistically significant correlation between allergen-spec ific IgE and the wheal area elicited by the same allergen, and a significan t correlation was found between the wheal elicited by 10 mg/ml histamine an d both the concentrated and diluted allergens (up to the sixth dilution). I n polysensitized patients, the allergen producing the largest wheal when us ed in concentrated form did not produce the same result when diluted. The s kin prick test with low-potency allergens was reproducible in individual pa tients even after a 7-day interval up to a 1:256 dilution of the commercial extract, although there was no clear correlation with allergen-specific Ig E concentration. In polysensitized patients, the use of high-potency or low -potency allergens for skin prick tests can lead to different conclusions r egarding the relative importance of each allergen.