The proposed study intends to compare the outcome of food challenge in hazelnut allergic patients with the outcome of basophile activation tests using hazelnut extract and components.

Accurate diagnosis of food allergy depends on food challenge outcome. The proposed study intends to compare the outcome of food challenge in hazelnut allergic patients with the outcome of basophile activation tests using hazelnut extract and components to evaluate the diagnostic utility of basophile activation testing.

With a view towards improved in vitro diagnostic methods, the investigators intend to evaluate the diagnostic potential of basophile activation testing in patients with hazelnut allergy confirmed by a positive provocation or supported by a convincing history of anaphylactic reaction(s) to hazelnut in the past, patients with pollinosis but no symptoms of hazelnut allergy and non-atopic control subjects.

Inclusion Criteria:

Primary Inclusion criteria:

• Male and female subjects, age ≥ 14 years
• Informed Consent as documented by signature

Secondary inclusion criterion

• Group A: positive case history of allergic reaction(s) to hazelnut positive double-blind placebo-controlled food challenge with hazelnut or positive titrated open food challenge with hazelnut or unambiguous case history of an anaphylactic reaction after hazelnut will be included without provocation
• Group B:positive skin test (SPT) with birch pollen and hazelnut and negative food provocation with hazelnut.
• Group C: negative case history of hazelnut and birch allergy and negative skin test (SPT) with hazelnut and birch pollen and negative food provocation with hazelnut

Exclusion Criteria:

• Drugs not allowed due to interference with the food challenge (or shortest interval between last treatment and food challenge): corticosteroids systemically (2 weeks), antihistamines (3 days), beta blocker (1 day), angiotensin converting enzyme (ACE) inhibitors (2 days), omalizumab (2 months)
• Women who are pregnant
• Lack of safe contraception
• Uncontrolled asthma, forced expiratory volume (1 second) <70% predicted value
• Acute allergic disease
• Chronic urticaria
• Mastocytosis
• Other clinically significant concomitant disease states
• Known or suspected non-compliance, drug or alcohol abuse,
• Inability to follow the procedures of the study
• Participation in another study with investigational drug within the 30 days preceding and during the present study

In terms of study inclusion there will be no masking. Only the food challenge itself will be masked.