Plasmin Generation Analysis in Patients with Bleeding Disorder of Unknown Cause.

Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion after evaluation of plasma coagulation and platelet function. The underlying mechanisms are unclear, but increased fibrinolysis and abnormal clot formation may play a role. All BDUC patients (n=375) from the Vienna bleeding biobank were analyzed in comparison to healthy controls (HC, n=100) in this case-control study. Plasmin generation (PG) parameters were analyzed using calibrated fluorescence detection in citrated-plasma samples. Turbidimetric plasma clot formation/ lysis of 293 (78%) BDUC patients and confocal microscopy of clots from representative BDUC patients (n=6) and HC (n=9) were assessed. Fibrinolytic factors were measured using commercially available ELISAs. In PG analysis, BDUC patients exhibited lower velocity and peak plasmin, but a higher endogenous plasmin potential compared to HC. Peak plasmin correlated with maximum clot absorbance, but not with clot lysis time. Clot absorbance is an indicator of clot fiber density. Confocal microscopy analysis revealed that BDUC patients' clots had a tendency towards thicker fibers, which negatively correlated with peak plasmin (r=-0.561, p=0.030). Peak plasmin correlated weakly with FXIII, but not with the other fibrinolytic factors (alpha2-antiplasmin, thrombin activatable fibrinolysis inhibitor or plasminogen activator inhibitor 1) or bleeding severity. A model comprising fibrinogen and parameters of PG yielded high predictive power in discriminating BDUC patients from HC during 5-fold stratified cross validation (80% of data, mean AUC: 0.847). The same model generalized well to unseen data (20% of data, AUC: 0.856). Overall, BDUC patients exhibited counterintuitively reduced peak plasmin, potentially related to altered clot structure.