686 The validity of a novel patient-operated device for measuring skin barrier function

      Transepidermal water loss (TEWL) and surface capacitance measure skin barrier permeability and skin hydration, respectively, and are frequently utilized in atopic dermatitis clinical trials. Conventional devices used to measure TEWL and hydration are often costly, bulky, and technically challenging, limiting their use to tertiary care facilities and research centers. GPSkin, a novel commercially-available device measures TEWL and skin hydration utilizing a compact, low-cost probe designed for patient operation and functions via smartphone application. This study investigated the correlation of this novel device with the Biox AquaFlux and Courage-Khazaka Corneometer, as well as the reliability of these devices, at a single institution. Two measurements per device were taken on the left volar forearm. Participants performed their own measurements with GPSkin while study personnel collected the remainder of data. Climate was controlled to 20-22°C and 30-50% humidity. Participants (n=50) abstained from moisturizing and bathing for at least 6 hours prior to measurements. GPSkin and the AquaFlux demonstrated moderate correlation by Spearmans (rs=0.48, p=0.0004). GPSkin and the Corneometer demonstrated moderately strong correlation (rs=0.63, p=Additional analyses were performed removing measurements with a >4-fold difference in repeated values, all within the GPSkin TEWL measurements. Excluding these outliers (n=42), GPSkin TEWL ICC improved to 0.54 (95% CI: 0.29-0.72) and correlated better with the AquaFlux (rs = 0.52, p=0.0004). Results from this study suggest a future role for this novel device in barrier studies or for patient-directed skin barrier measurement. Additional study of outlier data may identify strategies to optimize device reliability.