The objective of this study is to determine the biologic activity of a Chenopodium album 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.

Four concentrations of Chenopodium album 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.
• Positive skin prick test with a standardized commercially available preparation of chenopodium album allergen extract.
• A positive test for specific IgE to chenopodium album (CAP-RAST major or equal to 2).
• Allergic symptoms during the pollen season of Chenopodium album.
• Medical history positive allergy inhalation (rhinitis and /or rhinoconjunctivitis and/or asthma) from Chenopodium album.

Exclusion Criteria:

• Immunotherapy in the past 5 years with an allergen preparation known to interfere with the allergen to be tested.

• Use of drugs that may interfere with the skin reactions (e.g., antihistamines).

• Treatment with any of the following medications: tricyclic or tetracyclic

  o IMAOs antidepressants,b-blockers or chronic use of corticosteroids or oral or use of corticoids both via oral or parenteral, in repeated patterns and intermittent (> 10 mg/día de 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.