The effect of unmeasurable endogenous plasma factor activity levels on factor VIII dosing in patients with severe hemophilia A

BACKGROUND: Patients with hemophilia A are defined as "severe" if they present <0.01 IU mL^-1 of clotting factor VIII (FVIII) activity endogenously (i.e. in absence of FVIII concentrate administration). However, an exact measurement of baseline FVIII is often impossible in such patients as the lower limit of quantification for most FVIII assays is around 0.01 IU mL^-1, forcing assumptions to be made regarding endogenous circulating level.