Validation of the Skin Prick Automated Test (SPAT) Cut-Off Value in Birch Pollen and House Dust Mite Allergic Rhinitis Patients.

Introduction: A novel device, Skin Prick Automated Test (SPAT), previously showed reduced variability and more consistent test results compared to conventional skin prick test (SPT) to identify allergic sensitisation. This study aimed to clinically validate the adjusted SPAT cut-off in patients with confirmed birch or house dust mite (HDM) allergy.

Methods: Seventy-five adults were included: 25 non-allergic subjects (confirmed by lack of allergy history and negative SPT), 25 birch and 25 HDM allergic rhinitis patients (both confirmed by positive SPT and nasal allergen challenge [NAC]). All subjects received a conventional SPT and an automated SPT for B ver, D pter, D far and control solutions.

Results: A cut-off of 4.2 and 4.1 mm, respectively, resulted in the highest accuracy to detect birch or HDM allergy using SPAT. Referring to previous study results suggesting a reliable cut-off value of 4.5 mm, it was decided to maintain 4.5 mm as SPAT cut-off indicating allergic sensitisation. Accuracy did not significantly differ between SPAT (96% using 4.5 mm) and conventional SPT (98% using 3.0 mm) to detect HDM allergy or to detect birch pollen allergy (100% for SPAT and SPT). SPAT wheal measurements performed through a ruler on the forearm or through digital measurement on a composite image did not significantly differ for any of the patient groups analysed.

Conclusion: SPAT showed an equivalent accuracy to detect birch pollen or HDM allergy compared to conventional SPT, using the adjusted 4.5 mm SPAT cut-off in patients with confirmed allergic rhinitis. The SPAT web viewer can be used easily and effectively for digital wheal measurement on a composite image.