Skin prick test (SPT) is a first line diagnostic test to detect type I hypersensitivity in patients suspected of an inhalant allergy. A novel S.P.A.T. or Skin Prick Automated Test device has been developed to enable more standardised allergy testing. In two independent studies, Gorris and colleagues previously showed that test results after S.P.A.T. are less variable and more consistent compared to conventional skin prick testing (Gorris et al. Allergy. 2023; Seys et al. Rhinology 2024). In these studies conducted in volunteers, a cutoff value of 4.5 mm has been proposed based on the 97.5 percentile level of glycerol control wheals.

The current study aims to determine a cutoff value corresponding to the highest accuracy to discriminate between sensitized-allergic and non sensitized, non allergic subjects for both house dust mite and birch allergens.

Inclusion Criteria:

• Provide informed consent signed by study patient and investigator;
• Subjects with Health Social Identification Number;
• Allergic subjects with rhinitis with or without asthma and with or without conjunctivitis symptoms with proof of sensitisation to an inhalant allergy, either house dust mite ( Dermatophagoides pteronyssinus) or birch pollen by a positive skin prick test (SPT) with a wheal diameter ≥3 mm as compared to negative control. The clinical response against the culprit allergen will be assessed by a positive nasal allergen provocation test. (patients must not have clinical symptoms corresponding to both sensitization).
• Non-allergic subjects with proof of lack of sensitisation to any of the above referred allergens by a negative conventional skin prick test less than 2 years.
• Normal lung function as judged by investigator with FEV 1 and FEV 1/FVC ≥ 70% of predicted
• Willing and able to comply with clinic visits and study-related procedures;
• Able to understand and complete study-related questionnaires.

Exclusion Criteria:

• Skin pathology like chronic or exuberant urticaria, dermographism, chronic dermatitis that needs daily treatment;
• Any skin abnormalities, which could negatively - in the opinion of the investigator - affect the test results, including large scars and tattoos on the forearm ;
• Patients with clinical symptoms corresponding to both sensitization to birch and house dust mite
• Use of antihistaminic medication < 7 days before the start of the study;
• Use of tricyclic antidepressants (antihistamine activity) < 7 days before the start of the study;
• Use of topical (on the forearm) or systemic corticoids < 7 days before the start of the study;
• Use of any monoclonal antibodies such as omalizumab, dupilumab, mepolizumab < 6 months before the start of the study;
• Use of oral systemic corticosteroids within 4 weeks prior to screening
• Use of intramuscular systemic corticosteroids within 3 months prior to screening
• Use of allergen immunotherapy for the allergen tested (<2 y) or another inhalant allergen;
• Pregnancy or breastfeeding;
• Women without highly effective contraception (hormonal contraception, intrauterine device, bilateral tubal occlusion/ligation, vasectomized partner, sexual abstinence) at least one month prior to inclusion and during the study;
• Incapacitated subjects;
• Subjects who do not speak the local language (French);
• Subjects who cannot read or write.