Validation of a Skin Prick Automated Test (SPAT) cutoff value in birch pollen and house dust mite clinically allergic patients
Sven Seys (Leuven, Belgique), Alina Gherasim (Strasbourg, France), Florian Odul (Strasbourg, France), Zuzana Diamant (Groningen, Pays-Bas), Philippe Gevaert (Gent, Belgique), Peter Hellings (Leuven, Belgique), Dirk Loeckx (Aarschot, Belgique), Senne Gorris (Aarschot, Belgique), Frédéric De Blay (Strasbourg, France)
Background

Skin prick test (SPT) is the gold standard for identifying allergic sensitization in individuals with a suspected airborne allergy. A novel device, Skin Prick Automated Test (SPAT), previously showed reduced variability and more consistent test results compared to conventional SPT (Gorris S, Allergy, 2023; Seys SF, Rhinology, 2024). Based on previous clinical data, an adjusted SPAT cutoff value of 4.5mm has been suggested.This study aimed to validate the adjusted SPAT cutoff value in birch pollen and house dust mite (HDM) allergic patients confirmed by a positive nasal allergen provocation test (NAPT).

Method

75 adults (18-59 years) were recruited for this study: 25 non-allergic subjects (confirmed by no allergy history and negative SPT for birch pollen, dermatophagoides pteronissinus (d pter), d farinae (d far)), 25 birch pollen allergic patients, 25 HDM allergic patients (both confirmed by positive NAPT and SPT). NAPT was considered positive if a Lebel score of 5 or a drop of 40% in Peak Nasal Inspiratory Flow (PNIF) was reached. All subjects received a conventional SPT (left arm) and automated SPT (right arm) for birch, d pter, d far and control solutions.

Results

A cutoff value of 4.5mm had the highest level of accuracy to detect either true birch pollen or HDM- allergic patients using SPAT. Sensitivity and specificity of SPAT to detect birch sensitization (equal or higher than 4.5mm) were both 100%, and 92% and 100%, respectively, to detect HDM sensitization. Similarly, sensitivity and specificity of conventional SPT (equal or higher than 3.0mm) to detect birch pollen sensitization are both 100%, and 96% and 100%, respectively, to detect HDM sensitization. Wheal measurements after SPAT performed through a ruler on the patient’s forearm or through a composite image on a web viewer did not significantly differ for any of the patient groups analysed.

Conclusion

SPAT shows a comparable accuracy to detect birch pollen or HDM sensitization to conventional SPT using the adjusted 4.5mm cutoff value in patients with a clinically relevant allergy. The SPAT web viewer can be used easily and effectively for wheal measurement on a patient’s forearm through a composite image.