Evaluation of Methods for the Estimation of Threshold Concentrations by the Skin Prick Test

The allergen dose-response curve is flat; thus, small changes in wheal size reflect large differences in skin sensitivity. The sensitivity as measured by provocation tests is given by the threshold concentration that causes symptoms and/or objective signs. The threshold concentrations differ by several magnitudes between the most and the least sensitive individuals clinically allergic to the same allergen. Variation in technique can be minimized by relating allergen responses to that to histamine. The aim here is to present and validate simple methods for estimation of the skin sensitivity given as the concentration inducing a wheal of the same size as that with the positive reference, 10 mg/ml of histamine HCl, in the same patient.