Immunoassay-based biomarkers in atopic dermatitis

Atopic dermatitis (AD) is a persistent and recurring inflammatory skin condition that affects 204 million people worldwide, with prevalence rates of 11.1 % among children and 6.3 % among adults. This condition affects multiple systems, resulting in pruritus, skin barrier defects, and a Th2-driven immune imbalance, which consequently leads to significant costs and a diminished quality of life. To enhance precision medicine in laboratory diagnostics, it is essential to identify a neutral biomarker that can complement traditional severity assessments, such as SCORAD and EASI, for the diverse phenotypes and endotypes of AD. This narrative review examines immunoassay-based biomarkers with proven clinical validity in diagnostic laboratory medicine. Biomarkers such as TARC/CCL17, IL-13, IL-22, IL-31, SCCA1/SCCA2, and periostin are assessed using various tests, including ELISA, bead-based multiplexing, proximity extension, and highly sensitive digital methods. The samples included serum, plasma, and skin samples obtained through tape-stripping and microneedle collection. The parameters for analytical validation included detection and quantification limits, reportable range, precision, linearity, carryover effects, method comparison, interference assessment, heterophile antibody effects, calibration, and external quality standards. Clinical performance assessment uses measures such as the area under the curve (AUC), likelihood ratios, and decision limitations. Conventional biomarkers, including total IgE, peripheral eosinophil count, and tryptase, show less clinical utility than new biomarkers. Critical implementation requirements include standardized skin sample collection methods, population-specific reference intervals, inter-platform harmonization, and consensus-based cut-off values with clinical significance. This review outlines an evidence-based plan for incorporating reliable AD biomarker tests into current diagnostic methods to facilitate precise skin treatment and personalized care.