Validation of a novel patient-operated device for measuring skin barrier function in atopic dermatitis

Background: Transepidermal water loss (TEWL) and capacitance are used in atopic dermatitis (AD) trials to provide objective data on clinical change and response to therapy. Many barrier devices are costly, limiting their utility. GPSkin is a novel low-cost, patient-operable device that measures both TEWL and capacitance via smartphone application. Objective: This validation study investigated the correlation of GPSkin with the AquaFlux and Corneometer, and the reliability of these devices, in patients with AD. Methods: Fifty AD patients with varying disease severity performed self-measurements with GPSkin, while investigators collected data with all 3 devices, on both nonlesional and lesional skin. Conclusion: GPSkin and AquaFlux demonstrated strong correlation for TEWL on nonlesional and lesional skin by Spearman's correlation (r_s), independent of device user. For capacitance, GPSkin and the Corneometer showed moderate correlation when obtained by patients, yet a strong correlation when obtained by a clinician. Despite good correlation, GPSkin showed poor agreement with both the AquaFlux and Corneometer in Bland-Altman plots. GPSkin underestimated both TEWL and capacitance. Overall, the devices had good test-retest reliability. None of the devices could discriminate between AD severity states. While GPSkin marks an exciting advancement in barrier technology, further study is needed for validation on AD skin.