In vivo recovery of factor VIII following transfusion: a survey of recent data and publications to assess the influence of standards used for potency assignment. On behalf of the Subcommittee on Factor VIII and IX of the Scientific and Standardization Committee of the ISTH.

In the therapy of factor VIII deficiency, experience has taught the value of achieving a target level of plasma coagulation factor VIII. There is a consensus that an empirical value of 2 iu/dl/iu/kg may be used to estimate recovery, and hence plasma levels, of factor VIII. This may be influenced by the methods used to assign label potency to the products and for assessment of patient post-infusion plasmas. To assess a possible influence of the standard used to assign product potency on in vivo recovery, a survey was undertaken of recent in vivo recovery studies. Analysis of submitted data, in combination with published studies over the last ten years, revealed a significant influence of the standard used to assign potency to products on the measured in vivo recovery. Furthermore, from limited data the potency determined in post-infusion patient plasmas was found not to be influenced by the use of one-stage or chromogenic assay methods.