University of Twente Student Theses


The effect of the injection depth and injection volume on the wheal size in the Skin Prick Test

Jong, J.E. de (2023) The effect of the injection depth and injection volume on the wheal size in the Skin Prick Test.

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Abstract:Introduction Allergies affect a significant part of the paediatric population. Allergy diagnosis is based on clinical symptoms and the patient’s history, which can subsequently be confirmed by the Skin Prick Test (SPT). Although the SPT is a frequently used diagnostic tool in allergy practices, the results can be affected by a variety of performance factors. Therefore, this study aims to relate the injection depth and injection volume to the wheal size in the SPT to improve the reproducibility and reliability of the test in the future. Method The injection depth was investigated in clinical practice to gain insight into the forces applied on the lancet during the SPT. A soft and hard prick were defined by measuring the force applied on the lancet done by four medical assistants. Thereafter, experiments on ex vivo skin were executed to explore the relation between the injection depth and injection volume using OCT and fluorescence. The effect of the injection depth on the wheal size was also investigated by performing the SPT on healthy volunteers. The wheal size induced by a soft and hard prick were statistically compared by a paired samples T-test. At last, direct and indirect injections in agarose gel were compared using the needle-free injector as an alternative for the lancet in the future. Results A soft prick was defined as 5 grams and a hard prick as 60 grams and these values were used during the experiments in this study. The results of the ex vivo skin experiments showed contradictory results and a low correlation between the injection depth and volume was found. The study in healthy volunteers showed a significant difference between the mean wheal sizes induced by a soft prick 3.98 mm2 versus a hard prick 5.82 mm2 (p < 0.001). Conclusion The findings suggest that an increase in injection depth leads to an increase in wheal size. This could result in false negative SPT results, overdiagnosis or medicalisation. Therefore, it is highly recommended to standardise the SPT performance to obtain reproducible and reliable SPT results. Future research must focus on exploring devices to standardise the SPT performance, for example an auto-injector or needle-free injector.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:33 physics, 44 medicine
Programme:Technical Medicine MSc (60033)
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