Activation profiles of factor VIII in concentrates reflect one-stage/chromogenic potency discrepancies

We have investigated the possibility that differences in the profile of factor VIII (FVIII) activation, by thrombin, may help to explain the one-stage/chromogenic potency discrepancies in two therapeutic concentrates. A Method M concentrate and a recombinant B-domain-deleted (B-DD) concentrate were found to have one-stage/chromogenic ratios of approximately 1.15 and 0.70, respectively, relative to the World Health Organization (WHO) 6th International Standard (IS) FVIII concentrate, whether pre-diluted in FVIII-deficient plasma or buffer (+/- von Willebrand factor, VWF). The activation of FVIII, by thrombin, was followed in a buffer medium (+/- VWF) and all three concentrates showed similar times to reach peak FVIII coagulation (FVIII:C) activity. However, despite the use of equivalent amounts of FVIII:C for all three concentrates, the B-DD concentrate reached a higher peak level and maintained higher FVIII:C compared with the WHO 6th IS throughout the incubation period, whereas the Method M concentrate reached a lower peak level and maintained lower FVIII:C throughout the incubation period. We propose that the higher levels of FVIII:C found with the B-DD concentrate and the lower levels with the Method M concentrate, following activation, may be reflected in the potencies obtained by the chromogenic method and may be consistent with one-stage/chromogenic ratios of < 1.0 and > 1.0 respectively.