Abnormal whole-blood viscoelastic test results in patients with bleeding disorder of unknown cause

• Viscoelastic testing of whole blood identifies delayed clot formation and altered fibrinolysis, distinguishing BDUC patients from controls. • ROTEM parameters discriminate BDUC patients vs. healthy controls well but do not predict bleeding severity or bleeding risk. Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion in patients with a clinically relevant bleeding tendency. While BDUC patients often display bleeding phenotypes similar to those with other established mild to moderate bleeding disorders, global assays to identify BDUC or predict bleeding severity are lacking. Diagnostic utility of non-activated rotational thromboelastometry (ROTEM) in patients with BDUC and its association with bleeding severity and risk of future bleeding was assessed. In total, 464 patients with BDUC from the Vienna Bleeding Biobank were compared to 100 age-matched healthy controls. ROTEM was performed within one hour of sampling. The assessed parameters included clotting time (CT), clot formation time (CFT), maximum clot firmness (MCF), maximal lysis (ML), and area under the curve (ROTEM-AUC). Overall, we observed a delayed clot formation process with reduced lysis potential resulting in a larger ROTEM-AUC in BDUC patients. Compared to controls, BDUC patients exhibited prolonged CT (median 634.0 vs. 617.5 seconds, p