Clinical and Immunological Associations of Plasma Platelet-Activating Factor in Chronic Spontaneous Urticaria

Background/Objectives: Chronic spontaneous urticaria (CSU) is a heterogeneous immune-mediated condition involving multiple inflammatory pathways. The clinical utility of platelet-activating factor (PAF) as a biomarker in CSU remains insufficiently defined. This study aimed to evaluate plasma PAF levels in patients with CSU and to investigate their associations with clinical characteristics, disease activity, and laboratory and immunological parameters. Methods: This cross-sectional study included 205 adult patients diagnosed with CSU between January 2016 and May 2023. Clinical data, patient-reported outcome measures (PROMs), and extensive laboratory parameters were collected. Plasma PAF levels were measured using ELISA in 171 patients. Associations were analyzed using appropriate statistical methods. Results: The cohort was predominantly female (77.6%), with a mean age of 42.6 ± 15.3 years. Most patients had uncontrolled disease (76.9%). The median Urticaria Activity Score over 7 days (UAS7) score was 14, corresponding to mild disease activity. PAF levels differed significantly across clinical subgroups. Higher PAF levels were observed in patients with angioedema (alone or in combination with urticaria) compared to those with urticaria alone (p = 0.002), and in patients with predominantly nocturnal and early morning symptoms (p = 0.018). No associations were found between PAF levels and disease activity scores or treatment response. PAF levels showed positive correlations with age, age at symptom onset, IgM, IgG anti-IgE, HSP70, and the CD4/CD8 ratio (all p < 0.05). Conclusions: Plasma PAF levels are associated with specific clinical phenotypes, circadian symptom patterns, and selected immunological markers in CSU, suggesting that PAF may serve as a marker of underlying biological heterogeneity and immune activation. However, the present cross-sectional findings do not establish clinical utility, prognostic significance, or predictive relevance for treatment response, and these aspects require further longitudinal investigation.