Development of a Detection Method for Soluble Urokinase-Type Plasminogen Activator Receptor and Its Application in Predicting Prognosis of Severe COVID-19.

Identifying sensitive and specific blood biomarkers for early warning of severe COVID-19 remains a critical clinical need. Based on previous findings of elevated cytokines in bronchoalveolar lavage fluid and blood, we developed a novel luciferase immunosorbent assay (LISA) that selectively quantifies biologically active full-length suPAR and can eliminate interference from inactive fragments measured by conventional ELISA. Compared with conventional ELISA, LISA showed a lower detection limit (5.08 vs. 45.72 pg/mL) and a wider linear range (45.72-100,000.00 vs. 1234.46-11,111.11 pg/mL). In adult COVID-19 patients, suPAR levels were significantly elevated in severe cases (p < 0.001) and correlated positively with NLR and SII (p = 0.003 for each), and with IL-6 (p < 0.001), but negatively with lymphocyte count (p = 0.004). suPAR outperformed conventional inflammatory markers in predicting severe disease (AUC = 0.785) and adverse outcomes (AUC = 0.912), supporting its role as an independent predictor. In paediatric COVID-19 patients, suPAR remained superior to other single peripheral blood biomarkers for severity prediction, despite weaker correlations with inflammatory indices. This study establishes a reliable method for quantifying functionally intact suPAR and demonstrates its age-dependent predictive value, highlighting its potential for individualized risk stratification in COVID-19 patients.