The objective of this study is to determine the biologic activity of a Dermatophagoides pteronyssinus allergen extract in histamine equivalent prick (HEP) units, in order to be used as in-house reference preparation (IHRP).

This is an open, unblinded and non-randomized biological assay. The study design is a slight modification of the recommendations proposed by the Nordic Guidelines.

Three concentrations of Dermatophagoides pteronyssinus allergen extract, together with a positive and negative control, using 10 mg/ml histamine dihydrochloride solution and a glycerinated phenol saline solution, respectively, will be tested in every patient in duplicate on the volar surface of the forearm.

Inclusion Criteria:

• Subject has provided written informed consent, appropriately signed and dated by the subject (or legal representative, if applicable).
• Subject can be male or female of any race and ethnic group.
• Age > and =18 years and < and =60 years at the study inclusion day.
• Medical history of allergy with respiratory symptoms (rhinitis and /or rhinoconjunctivitis and/or asthma) to Dermatophagoides pteronyssinus.
• Positive skin prick test with a standardized commercially available preparation of Dermatophagoides pteronyssinus allergen extract. The skin prick test will be considered positive if the test results in a wheal major diameter of at least 3 mm or an area at least 7 mm2. Positive skin prick test results are valid if performed within one year prior to the inclusion of the subject in the study
• A positive test for specific IgE to Dermatophagoides pteronyssinus (CAP-RAST major or equal to 2). IgE results are valid if performed within one year prior to the inclusion of the subject in the study.

Exclusion Criteria:

• Immunotherapy in the past 5 years with a Dermatophagoides pteronyssinus allergen extract or other mites allergen extracts known to interfere with the allergen to be tested, due to a high degree of cross-reactivity.
• Use of drugs that may interfere with the skin reactions (e.g., antihistamines). See Appendix 1 of the protocol.
• Treatment with any of the following medications: oral tricyclic or tetracyclic antidepressants or IMAOs, beta-blockers, chronic use of corticosteroids or use of oral or parenteral corticosteroids in repeated and intermittent patterns (10 mg/daily of prednisone or equivalent).
• Women who are pregnant or period of breastfeeding and women with a pregnancy test positive during the visit 2, prior to the prick test.
• Dermographism affecting the skin area at the test site at either study visit.
• Atopic dermatitis affecting the skin area at the test site at either study visit.
• Urticaria affecting the skin area at the test site at either study visit.
• Diseases of the immune system relevant clinically, both autoimmune and immunodeficiencies.
• Serious diseases not controlled that may increase the risk for the safety of the subjects involved in this study, including, but not limited to the following: heart failure, uncontrolled or severe respiratory diseases,endocrine diseases, clinically relevant kidney or liver diseases or hematological diseases.
• Participation in any other clinical trial within 30 days (or 5 times the biological half-life of the research of the study product, whichever is longer) prior to the inclusion of the subject in this clinical trial.
• Patients with diseases or conditions that limit the use of adrenaline (heart disease, severe hypertension...)
• Severe psychiatric, psychological or neurological disorders
• Abuse of alcohol, drugs or medicines in the previous year.