CO-36 | PLATELETS MATTER: THROMBIN GENERATION IN PLATELET‐RICH-PLASMA VS. PLATELET‐POOR‐PLASMA UNDER NON-REPLACEMENT THERAPIES IN HEMOPHILIA

Abstract

Background and Aims. Non-replacement therapies have transformed the management of Hemophilia A (HA) and B (HB). Emicizumab (Emz) is a recombinant bispecific monoclonal antibody that mimics activated FVIII (FVIIIa), restoring FX activation and thrombin generation. Concizumab (Concz) is an anti–tissue factor pathway inhibitor (TFPI) monoclonal antibody that enhances thrombin generation by inhibiting the TFPI anticoagulant pathway, compensating for FVIII and FIX deficiencies. Although their mechanisms are well established, their interaction with cellular coagulation components, particularly platelets, remains poorly characterized. Platelets provide a procoagulant phospholipid surface and amplify thrombin generation, but their contribution in patients receiving non-replacement therapies is not fully understood. This study evaluated the role of platelets in patients treated with Emz or Concz by comparing thrombin generation assay (TGA) parameters in platelet-rich plasma (PRP) and platelet-poor plasma (PPP).Materials and Methods. Among 21 patients on Emz prophylaxis and 2 on Concz prophylaxis (in the Novo Nordisk study NCT04082429) followed at our center, blood samples were obtained from 15 patients with severe HA, with or without inhibitors, receiving stable Emz prophylaxis, and from 2 patients receiving Concz (one with severe HA and one with severe HB). Thrombin generation was assessed in PRP and PPP using the ST Genesia® system (Stago, Asnières-sur-Seine, France). Frozen PPP samples were analyzed with the standard protocol, whereas PRP samples were tested within 2 hours of collection using an in-house validated protocol. Evaluated parameters included Lag Time, Peak Height, Time to Peak, Endogenous Thrombin Potential (ETP), Velocity Index, and Start Tail. PRP and PPP results were compared to assess platelet contribution to thrombin generation.Results. Six samples were excluded due to instrument malfunction. A comparison between PRP and PPP in the 11 evaluable patients is reported in Table 1. In all patients, PRP showed increased lag time, time to peak, ETP, and start tail, together with reduced velocity index, while peak height showed no consistent trend. No relevant differences in thrombin generation profiles were observed between patients treated with Concz and those receiving Emz.Conclusions. Consistent differences between PPP- and PRP-based TGA were observed across all patients. PRP curves showed delayed thrombin generation onset and prolonged time to peak, associated with higher total thrombin generation and increased endogenous thrombin potential. These findings suggest that PRP-based TGA may provide a more comprehensive assessment of the hemostatic profile in patients receiving non-replacement therapies by capturing platelet-dependent coagulation mechanisms.