Is “Physiological Lysis” in Viscoelastometry a Plasmin-Mediated Process?

Viscoelastic testing (VET) is widely used to guide hemostatic therapy in patients with coagulopathy. One important application is the detection of fibrinolysis, defined as a reduction in clot amplitude after maximum clot firmness (MCF), quantified as maximum lysis (ML). Low ML values have recently been associated with adverse outcomes in trauma and sepsis. However, the biological basis of low ML remains unclear. Objective: To determine whether low ML values reflect reduced plasmin-mediated fibrinolysis in tissue factor (TF) activated viscoelastic assays (EX-assay). Methods: A total of 120 healthy adults (52.5% female; mean age 38.2 ± 14.1 years) were studied. EX-assay without fibrinolysis inhibition were compared with assays containing the antifibrinolytic agent tranexamic acid (AP-assay). VET parameters obtained with and without fibrinolysis inhibition were compared using paired analyses, Pearson correlation, and Bland–Altman methods. Results: Clot firmness at 10 min (CA10) was similar with or without fibrinolysis inhibition; although MCF differed statistically, the difference was clinically negligible. ML ranged from 1% to 13% in both assays, with nearly identical mean values (5.9 ± 2.6% vs. 6.0 ± 2.6%). Correlation analysis demonstrated strong agreement for CA10, MCF, and ML between assays, and Bland–Altman analysis confirmed minimal bias for ML. Conclusions: Low ML values in TF-triggered viscoelastic assays were unaffected by tranexamic acid, suggesting that they are unlikely to reflect plasmin-mediated fibrinolysis. These findings support the contribution of alternative mechanisms, such as platelet-mediated clot retraction.