Halo fluorescence fibrinolysis test: a novel quantitative assay to evaluate fibrinolysis on established plasma clots.

BACKGROUND: Fibrinolysis is essential for dissolving blood clots and maintaining hemostasis. This process is primarily mediated by tissue-type plasminogen activator, which converts plasminogen into plasmin, thereby breaking down fibrin clots. Traditional amidolytic assays often measure plasmin generation without directly assessing fibrin degradation, while thromboelastography frequently overlooks clot maturation, which significantly influences fibrinolysis resistance. OBJECTIVES: To address these limitations, we present a novel quantitative assay for analyzing fibrinolysis on established clots, termed the halo fluorescence fibrinolysis (HoFF) test. METHODS: The HoFF test used fluorophore-conjugated fibrinogen to form halo-shaped plasma clots. Fibrinolysis was induced with tissue-type plasminogen activator or its variant tenecteplase, and clot breakdown was monitored via real-time fluorescence detection by a microplate reader. The fluorescence signal was analyzed to calculate a fibrinolysis index, indicating fibrinolytic capacity. Its specificity for fibrinolysis over plasmin generation was validated against traditional amidolytic assays using a plasmin substrate. RESULTS: Fluorescence-labeled fibrinogen was confirmed as a reliable marker of fibrin degradation. The HoFF test exhibited strong linear correlations between the fibrinolysis index and plasminogen activator concentrations, with robust reproducibility. It also effectively evaluated tenecteplase-induced fibrinolysis and demonstrated versatility across clot types, including mouse plasma and human whole-blood models. Furthermore, the test distinguished fibrinolysis from plasmin generation, demonstrated by the differential effects of tranexamic acid inhibition. CONCLUSION: The HoFF test offers a sensitive, reliable, and high-throughput tool for quantitatively evaluating fibrinolysis on established human and mouse plasma and whole blood clots.