Fig. 1

Defining a standardized dose using the index of reactivity. An allergen extract termed the IHRP is said to have a concentration of 100 IR/mL when, during skin prick-testing using a Stallerpoint^® needle on 30 subjects who are sensitized to the corresponding allergen source, it triggers a wheal size of 7 mm (geometric mean). Codeine phosphate or histamine serve as positive controls (C+), and diluent only is used as a negative control (C−) and to assess any background effects unrelated to the allergen extract. IHRP in-house reference preparation; IR, index of reactivity