Intrinsic activated thrombin generation for treatment efficacy and monitoring of octocog alfa and emicizumab in severe hemophilia A

Background Monitoring patients with severe hemophilia A (SHA) receiving nonfactor replacement therapies such as emicizumab presents significant challenges, because conventional activated partial thromboplastin time-based assays are subject to interference from these treatments. Therefore, we hypothesized that an intrinsic activated thrombin generation assay (TGA) could be an improved alternative. Objectives To investigate the sensitivity and applicability of intrinsic activated TGA compared with extrinsic activated assays for monitoring SHA patients on factor (F)VIII (FVIII) and non-FVIII replacement products. Methods We developed a novel intrinsic trigger reagent (platelet-poor plasma [PPP] Reagent INT) and compared it with tissue factor (TF) reagents, as well as an FXIa-based reagent, using the Calibrated Automated Thrombography method. Thrombin generation was measured in deficient plasmas, healthy volunteers ( n = 103), FVIII-deficient plasma spiked with octocog alfa or emicizumab, and plasma from SHA patients on emicizumab ( n = 22). Results PPP Reagent INT specifically activated the intrinsic pathway, showing minimal thrombin generation in FXII- and FXI-deficient plasma, and no thrombin generation in FIX- and FVIII-deficient plasma, whereas activation occurred independently of prekallikrein. Linear regression analysis showed superior sensitivity for PPP Reagent INT triggered thrombin generation in FVIII-deficient plasma spiked with octocog alfa or emicizumab. In plasma from SHA patients, PPP Reagent INT demonstrated sixfold and fourfold greater sensitivity to emicizumab level changes compared with TF-based reagents. Conclusion Intrinsic activated TGA using PPP Reagent INT provides enhanced sensitivity for monitoring SHA patients on both FVIII and non-FVIII replacement products compared with TF-based triggers, representing a promising tool for personalized monitoring.