Background Patients with severe hemophilia A display varied bleeding phenotypes despite similar factor VIII (FVIII) activity levels. Objective We investigated different thrombin activatable fibrinolysis inhibitor (TAFI)‐related variables in patients with severe hemophilia A and their possible correlation with bleeding tendency. Patients/Methods Sixty‐one patients with severe hemophilia A (FVIII:C <1%], treated on demand, were included. Patients were categorized as mild, moderate, and severe bleeders according to number of bleeds per year (≤2, 3‐24, ≥25, respectively). Thirty healthy males served as controls. Clot lysis time was assessed by turbidimetric assay, TAFI activation by two‐stage functional assay, and response to TAFIa as the prolongation of fibrinolysis time upon addition of purified TAFIa. Circulating levels of activated TAFI (TAFIa/ai) were measured by specific enzyme‐linked immunosorbent assay. Results As compared to controls, hemophilic patients displayed shorter lysis time, less TAFIa generation, and reduced response to TAFIa, but similar TAFIa/ai levels. Clot lysis time was similar in mild, moderate, and severe bleeders, whereas TAFIa generation and response to TAFIa decreased with the increase in bleeding tendency; moreover, circulating TAFIa/ai levels were highest in severe bleeders. Patients with markedly impaired TAFIa generation or TAFIa response (below median) displayed 3‐fold to 4‐fold higher bleeding rate and factor consumption than patients whose TAFI‐related values approached the control ones. Conclusion The TAFI pathway impairment correlates with bleeding phenotype in severe hemophilia and may represent a promising tool to stratify the bleeding risk.

Introduction: Plasma-derived FVIII/VWF complex was reported to be less sensitive to inhibitors than FVIII preparations devoid of VWF. Aim: To compare the efficacy of FVIII/VWF complex (Fanhdi) and five different VWF-free FVIII preparations in restoring thrombin generation and activation of thrombin-activatable fibrinolysis inhibitor (TAFI) in haemophilic plasma, with and without inhibitor, and in cell-based models. Methods: Experiments were performed in haemophilic plasma supplemented with inhibitory IgG or in plasma samples obtained from haemophilia A patients without (n = 11) and with inhibitor (n = 12). Thrombin generation was evaluated by calibrated automated thrombography (CAT) under standard conditions, in the presence of activated protein C (APC) or thrombomodulin (TM), and in cell-based models including endothelial cells, either alone or in combination with platelets or tissue factor-expressing blood mononuclear cells. The kinetics of TAFI activation was determined by a two-stage functional assay in the absence and in the presence of APC. Results: In haemophilic plasma without inhibitor, Fanhdi enhanced thrombin generation and TAFI activation as well as recombinant (2nd-4th generation) and plasmaderived FVIII preparations devoid of VWF. On the contrary, in plasma with inhibitor, Fanhdi displayed a greater ability to restore thrombin generation and TAFI activation under all tested conditions. Notably, in cell-based models including endothelial cells, Fanhdi proved more efficient than all other preparations in improving thrombin generation even in the absence of inhibitor. Conclusion: The greater pro-haemostatic activity of FVIII/VWF complex, either in haemophilic plasma with inhibitor or in the presence of endothelial cells, may offer therapeutic advantages.