Head-to-Head Comparison Study Between Different FDA Registered Allergy Skin Test Applicators

Background and Rationale:

Percutaneous allergy skin testing remains the gold standard diagnostic method for IgE-mediated allergic disease. Multiple-head skin prick test (SPT) devices enable simultaneous application of multiple allergens, improving testing efficiency while potentially reducing patient discomfort. However, significant inter-device variability exists among commercially available devices, with important implications for diagnostic accuracy and clinical interpretation.

Intra-device variability-inconsistent responses across individual test heads within a single device-represents a particularly concerning phenomenon that may lead to physician misinterpretation and potentially inappropriate treatment decisions. Such variability can be attributed to manufacturing factors including tooling mold precision, molding equipment quality, and process controls during production. Prior research has demonstrated that devices with lower finished product variability exhibit improved clinical performance characterized by reduced false-positive reactions to negative controls.

Study Design:

This prospective, single-visit, head-to-head device comparison study employed a paired design in which each participant served as their own control, receiving testing with two devices simultaneously-one device applied to each forearm. This within-subject design minimizes inter-individual variability and provides robust comparative data.

Participants were allocated into two comparison groups based on device head configuration: a 10-head device comparison (n=13) and an 8-head device comparison (n=17). Device assignment to right versus left forearm was randomized. Testing personnel were blinded to solution contents (histamine versus glycerin) during application, and a separate evaluator blinded to device assignment recorded wheal measurements.

Study Procedures:

All testing was performed by trained personnel in accordance with standard percutaneous skin testing protocols. Histamine dihydrochloride (1 mg/mL; ALK-Abello) served as the positive control and glycerin solution (ALK-Abello) served as the negative control. Devices were applied to the volar forearm surfaces with standardized pressure and technique. Test sites were maintained at least 2 cm apart to prevent cross-contamination between histamine and glycerin reactions.

Wheal measurements were obtained 15-20 minutes post-application using the mean diameter method (average of longest diameter and its perpendicular midpoint), consistent with established international guidelines. Pain assessment was performed immediately following device application.

Statistical Considerations:

Paired comparisons between devices were analyzed using Wilcoxon signed-rank tests for continuous variables and McNemar's test for dichotomous outcomes. Intra-device variability was quantified using the coefficient of variation (CV) calculated across test heads, with lower values indicating greater consistency. Exact binomial (Clopper-Pearson) confidence intervals were calculated for sensitivity and specificity estimates. Statistical significance was set at α=0.05 (two-sided).

Clinical Significance:

This study addresses an important knowledge gap regarding comparative clinical performance of multi-head allergy testing devices. Results provide evidence-based data to inform device selection decisions that may impact diagnostic accuracy, patient comfort, and reliability of allergen identification in clinical allergy practice.