Automated Skin Prick Test at 4.5 mm Cut-Off Matches Accuracy of Traditional Method

A study showed that a 4.5 mm cut-off Skin Prick Automated Test had equivalent accuracy in detecting birch pollen or house dust mite allergy among patients with allergic rhinitis to the conventional skin prick test.1

“Using the [Skin Prick Automated Test] device in the current study, a cut-off value of 4.2 and 4.1 mm showed the highest accuracy to detect birch pollen or [house dust mite] allergy…” wrote investigators, led by Sven F. Seys, PhD, from Hippo Dx, Aarschot, Belgium.1 “The previously suggested cut-off value of 4.5 mm was based on the 97.5 percentile value of the longest wheal diameter after glycerol-saline pricks in over 100 volunteers. Given that one can barely discriminate between 4.2, 4.3 and 4.5 mm while measuring skin reactions, it was decided to maintain 4.5 mm as a reliable SPAT cut-off value.”

Skin prick testing has many benefits, including being safe, quick (results within minutes), high sensitivity, and low cost. However, a health care professional’s technique and the type of lancet they use can lead to variations in results. Research has shown that less variation occurs with the Skin Prick Automated Test, but it tends to lead to more wheals than the traditional skin prick test.

Due to these findings, experts suggested a 4.5 mm threshold to determine a positive result.2 Investigators aimed to confirm whether the 4.5 mm cut-off works in patients with birth pollen or house dust mite allergy.1 In the study, the team evaluated Skin Prick Automated Test cut-off values ranging from 3.0 to 6.0 mm with 0.5 mm increments.

The study included 75 adults with birch pollen allergy (n = 25; 64% females, mean age, 35.4 years), house dust mite allergy (n = 25; 60% female, 35.2 years), and no allergy (n = 25; 58% female, 33.3 years).1 Allergies were confirmed by a positive skin prick test and a nasal allergen challenge.

Among the house dust mite group, 76% had allergic rhinitis, 24% had allergic rhinoconjunctivitis, and 44% had allergic asthma. Moreover, the birch pollen allergy group had 92% with rhinoconjunctivitis, 8% with only allergic rhinitis, and 40% with allergic asthma.1

The study found 4.32- and 4.1-mm cut-offs on the Skin Prick Automated Test, respectively, had the greatest accuracy in detecting birch or house dust mite allergy among patients with allergic rhinitis. Since previous studies proposed a reliable cut-off value of 4.5 mm, and 4.3 and 4.5 mm are difficult to tell apart, investigators decided to keep 4.5 mm as the cut-off indicating allergic sensitization.1

The study showed accuracy did not significantly differ between Skin Prick Automated Test (96% using ≥ 4.5 mm) and conventional skin prick test (98% using ≥ 3.0 mm) to detect either birch pollen or house dust mite allergy. They also did not find significant differences in Skin Prick Automated Test wheal measurements, calculated by a ruler on the forearm or digital measurement on a composite image.1

Both tests gave correct results in 100% of the negative controls, finding no significant skin reaction. Compared with the standard prick test, with 100% correct scores for histamine controls, 98.6% had correct scores with the Skin Prick Automated Test.1

The birch pollen tests showed strong reactions in people allergic to birch pollen—but not in other groups—showing the test could accurately identify this allergy (100%). The house dust mite tests (D. pteronyssinus and D. farina) showed strong reactions in most patients with house dust mite allergies (92%) and no reactions in people without these allergies.1

The study reported no serious adverse events. During the study, 20% of patients from the birch pollen group and 16% from the house dust mite group were treated with oral antihistamines for nasal allergic responses. 1 patient from the Birch pollen group received topical antihistamines for an ocular response.1

“To conclude, introducing [Skin Prick Automated Test] into routine clinical practice may create a new standard in skin prick testing, reducing test variability while maintaining high sensitivity,” investigators concluded.1 “Validation of the [Skin Prick Automated Test] outcomes in allergic rhinitis patients with clinically relevant respiratory allergy now allows widespread use of the device both in research and clinical practice.”

References

1. Seys SF, Gherasim A, Odul F, et al. Validation of the Skin Prick Automated Test (SPAT) Cut-Off Value in Birch Pollen and House Dust Mite Allergic Rhinitis Patients. Allergy. Published online July 9, 2025. doi:10.1111/all.16645

2. Gorris S, Uyttebroek S, Backaert W, et al. Reduced intra-subject variability of an automated skin prick test device compared to a manual test. Allergy. 2023;78(5):1366-1368. doi:10.1111/all.15619