Serum Immunometabolic Biomarkers Reveal Distinct Phenotypes in Chronic Urticaria

Background/Objectives: Chronic urticaria (CU) is a heterogeneous inflammatory disorder generally attributed to mast cell activation. However, emerging evidence suggests that metabolic reprogramming and systemic immune dysregulation also contribute to the disease pathophysiology. This study aimed to investigate the interplay between epithelial barrier integrity, innate immune regulation, metabolic activity, and mast cell effector mechanisms in CU. Methods: Forty CU patients and 40 healthy controls were evaluated. Clinical parameters included disease severity, disease subtype, antihistamine response, IgE levels, anti-TPO status, gastrointestinal symptoms, and angioedema. Serum levels of histamine, intestinal fatty acid-binding protein (IFABP), soluble CD14 (sCD14), diamine oxidase (DAO), D-lactic acid, endotoxin, zonulin, calprotectin, and related ratios were measured. Disease activity and control were assessed using the UAS7 and UCT scores. Results: CU patients exhibited significantly higher DAO (p = 0.003) and lactic acid (p = 0.004) levels compared to controls, whereas other markers showed no significant differences. In anti-TPO-positive patients, sCD14 levels were reduced (p = 0.024), while histamine/sCD14 (p = 0.005), lactic acid/sCD14 (p = 0.014), IFABP/sCD14 (p = 0.008), and zonulin/sCD14 (p = 0.027) were significantly elevated, suggesting relative amplification of metabolic and barrier-related signals under impaired innate immune regulation. Severe anti-TPO-positive patients exhibited lower sCD14 (p = 0.022) and NLR (p = 0.013) but higher UAS7 (p = 0.032), histamine (p = 0.011), calprotectin (p = 0.041), and CD14-normalized ratios, including histamine (p = 0.003), IFABP (p = 0.028), lactic acid (p = 0.019), zonulin (p = 0.029), and calprotectin (p = 0.011) compared with severe anti-TPO-negative patients, indicating a mast cell-dominant and metabolically active inflammatory phenotype. The lactic acid/DAO ratio was significantly lower in controlled versus uncontrolled CU (p = 0.013) and showed discriminatory potential for disease control. Patients with angioedema had higher CRP (p = 0.038) and UAS7 scores (p < 0.001). Conclusions: CU exhibits marked immunometabolic heterogeneity. Elevated DAO and lactic acid indicate increased histamine turnover and metabolic activation, whereas altered sCD14-normalized biomarker profiles reveal immune dysregulation in anti-TPO-positive patients. Severe CU with features suggestive of thyroid autoimmunity manifests as a mast cell-dominant, metabolically active phenotype with relative suppression of innate immune modulators, contrasting with alternative pathways in other CU phenotypes. The lactic acid/DAO ratio may serve as a candidate biomarker of disease control. These results underscore the importance of phenotype-tailored therapeutic strategies in CU.