Improving allergy testing and diagnosis: impact of skin prick testing intra-head device variability on clinical performance

Document Type : Original Article


1 Lake Erie College of Osteopathic Medicine, Bradenton, FL, USA

2 MedScience Research Group, West Palm Beach, FL, USA

3 College of Biomedical Sciences, Larkin University, Miami, FL, USA


Background: Multiple head skin prick test (SPT) devices designed for percutaneous allergy testing suffer from intra-head device variability, which may lead to misinterpretations by testing physicians impacting allergy treatment. It is proposed that detailed, high-magnification inspection during the verification stage of the design and development process of SPT devices would improve clinical accuracy and performance. 
Objectives: This pilot study aimed to examine the impact of physical characteristics, including consistency of length and the precision of the tips of the applicator tines of two FDA commercially available SPT devices, on clinical performance. It was hypothesized that devices with lower finished product variability would improve clinical performance.
Methods: Visual inspection the Lincoln Multi-Test II (LM) and the ST-9® multiple head applicator (ST-9) were obtained by dimensional measurement using 160X magnification. A total of 8 subjects completed this pilot study. SPT with histamine (HIS; 1 mg/mL base) and saline glycerin (GLY) were applied on the volar surface of one forearm LM and ST-9 devices using on the opposite forearm. Data were obtained from 72 histamine sites for the ST-9 device and 64 histamine sites for the LM device with 72 negative control GLY sites recorded for the ST-9 device and 64 glycerinated GLY sites for the LM device.
Results: T-test revealed that the ST-9® employed a statistically significant shorter tine length (1.94 ± 0.02) and showed less variability of tine length (P < 0.05) compared with the LM (2.12 ± 0.03). The ST-9 showed a smaller tip diameter and significantly less tine point diameter variability (0.037 ± 0.006) (P < 0.05) compared to LM (0.042 ± 0.009). The ST-9 displayed significantly (P<0.05) less wheal reaction to the negative control glycerin GLY solution than LM.
Conclusion: The lower variability of ST-9® suggests less likely operator misinterpretations. Although considered an engineering design and manufacturing problem, precision and high magnification inspection during the verification stage of SPT devices may have important clinical implications. Studies on optimizing the magnification process to improve the precision and performance of SPT devices in the clinical setting are warranted.


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