Utility of Blood Biomarkers for Assessing Atopic Dermatitis Severity in Infants Aged < 2 Years

Background Atopic dermatitis (AD) is an increasingly common skin disease that can lead to serious morbidity in a subset of more severely affected infants. Thymus and activation‐regulated chemokine (TARC) and squamous cell carcinoma antigen 2 (SCCA2) are biomarkers. This study examined how severity, defined by Patient‐Oriented Eczema Measure (POEM) score, correlates with TARC, SCCA2, total immunoglobulin E (IgE), and eosinophil counts in infantile AD (< 2 years), comparing their diagnostic performance and examining each biomarker's association with individual POEM items. Methods This retrospective study included 50 children aged < 2 years with newly diagnosed AD (March 2023–November 2024). Patients were categorized as mild or moderate‐to‐severe disease based on POEM scores. Receiver operating characteristic (ROC) analyses were used to assess each biomarker's sensitivity and specificity for severity classification, and correlations with POEM's seven items were evaluated using Spearman correlations. Results SCCA2 had the highest diagnostic accuracy for mild AD (area under the curve [AUC] = 0.708), while TARC had the best performance (AUC = 0.717) for moderate AD. Total IgE and eosinophil counts had AUC values at approximately 0.5. TARC showed stronger correlations (Spearman's rank correlation coefficient [ r s] ≥ 0.4) with bleeding and flaking compared with SCCA2. Conclusions In children aged < 2 years with AD, TARC and SCCA2 were superior to total IgE or eosinophils in assessing severity. Both TARC and SCCA2 appear valuable for evaluating AD severity; a symptom‐specific biomarker selection may facilitate earlier diagnosis and targeted therapy. Larger prospective studies are needed to confirm these findings.