Modified clot waveform analysis to measure plasma coagulation potential in the presence of the anti-factor IXa/factor X bispecific antibody emicizumab

Background Emicizumab is an anti-activated factorIX/FX bispecific antibody that mimics activated FVIII cofactor function. Emicizumab does not require activation by thrombin, and its effect on shortening the activated partial thromboplastin time (APTT) is much greater than that of FVIII. Therefore, the APTT has limited utility in hemophiliaA (HA) patients treated with emicizumab. Aim To evaluate the global coagulation potential of emicizumab. Methods Clot waveform analysis (CWA) with prothrombin time (PT)/APTT mixed reagents was used to define hemostatic monitoring protocols in HA patients. A modified parameter, adjusted-vertical bar min1 vertical bar (Ad vertical bar min1 vertical bar), was developed. Maximum and minimum percentage transmittance were defined as 100% and 0% in the precoagulation and postcoagulation phases, respectively. Ad broken vertical bar min1 vertical bar was calculated as an index of the maximum velocity of the coagulation process. Results Ad vertical bar min1 vertical bar obtained with mixed-trigger reagent (PT/APTT/buffer, 1:15:135) in the presence of emicizumab optimally corresponded to the conversion rate estimated in animals; 0.2-0.4 IUdL(-1) equivalent FVIII per 1gmL(-1) emicizumab). Exvivo addition of emicizumab to HA plasma with or without inhibitors resulted in concentration-dependent increases in Ad broken vertical bar min1 vertical bar, with some individual variations. The addition of various concentrations of FVIII to HA plasma mixed with emicizumab resulted in dose-dependent increases in Ad vertical bar min1 vertical bar. Similarly, mixtures of activated prothrombin complex concentrate and emicizumab added to HA plasma resulted in dose-dependent increases in Ad vertical bar min1 vertical bar. In contrast, enhanced coagulation potential appeared to be better defined by the clot time than by Ad vertical bar mi1 vertical bar in experiments using recombinant activated FVII. Conclusion The PT/APTT reagent-triggered adjusted CWA could provide a useful means of assessing global coagulation potential in emicizumab-treated HA patients, with enhanced activity neither masking nor being masked by FVIII or bypassing agents.