Serum suPAR Associations with Clinical and Laboratory Variables and Emergency Department Disposition in Adults with Respiratory Symptoms: A Prospective Observational Cohort Study

Background: Soluble urokinase plasminogen activator receptor (suPAR) reflects systemic immune activation. We examined associations between serum suPAR and pulmonary/internal-medicine admission in adults presenting to the emergency department (ED) with respiratory symptoms. Methods: This prospective single-centre exploratory pilot included 87 adults (54 pathway admissions; 33 ED discharges). Serum suPAR concentrations were determined using four-parameter logistic calibration of an eight-point ELISA standard curve, with correction for the fivefold serum dilution. Exploratory adjusted logistic regression and single-marker ROC analyses were performed. Results: Median serum suPAR was 3440.0 (2497.5–4535.0) pg/mL overall, 3955.0 (2979.0–5559.0) pg/mL among admitted patients and 2832.5 (2216.0–3317.5) pg/mL among discharged patients (p < 0.001). The apparent AUC for suPAR was 0.765 (95% bootstrap CI 0.663–0.856). After adjustment for age-category midpoint, sex, SpO2 and log-CRP, the odds ratio for admission per 1-SD increase in log-suPAR was 2.43 (95% CI 1.18–4.98; p = 0.015); the corresponding estimate for log-CRP was 1.69 (0.93–3.07; p = 0.084). Conclusions: Serum suPAR was associated with pathway-specific admission after adjustment for CRP and selected clinical covariates. These exploratory findings do not establish incremental clinical utility and require external validation.