Allergen extracts are complex mixtures of proteins and contain varying amounts of allergenic and non-allergenic components. Many factors such as the biovariability, differences in extraction process and subsequent handling of allergens can affect the final composition, potency, and stability of allergen preparations. Genetic diversity of affected people adds another level of complexity. In order to control variability and to achieve consistency and reproducibility for optimal safety and sensitivity/specificity, it is essential to standardize the amount of allergen used in prick tests. Therefore, the system for biological standardization mainly used in Europe still is the biological calibration of in-House Reference Preparations (IHRP). The method has been adopted by the Nordic Council on Medicines as the Nordic Biological Unit, Histamine Equivalent Potency (HEP) or Skin Prick Test (SPT) value. The aim of this procedure is to estimate the biological activity of allergen extracts. The activity of an allergen extract is defined as 10,000 Diagnostic Biological Units (DBU) per ml (1 SPT per ml), when the extract provokes a specific skin reaction with a wheal of the same size as a wheal provoked by reference histamine at a concentration of 10 mg/ml, when both solutions are administrated using the same technique (prick testing) on at least 20 individuals who are clinically allergic and cutaneously reactive to the allergen concerned.

The present study aims to standardize the allergen extracts of Betula pendula, Phleum pratense and Dermatophagoides pteronyssinus by using this method.

• Trial with medicinal product

Inclusion criteria:

• Positive clinical history with inhalant allergy to at least one of the allergen to be standardized.
• At least one positive prick test (mean wheal diameter = 3mm) when tested with already standardized extracts of the allergens under investigation.
• Positive prick test (wheal diameter =3 mm) to Histamine 10 mg/ml
• Age: 18-60 years
• Written informed consent

Exclusion criteria:

• Diseases or medications, influencing the skin tests or that contradict the correct conduct and evaluation of the study.
• Pregnancy, skin irritations, drug and alcohol abuse and participation in another clinical trial within the last 30 days