FVIII activity (left axis) and inhibitor titer (right axis) from diagnosis to first partial remission. Shaded blue area represents the reference range for factor VIII activity; shaded orange area represents the reference range for the Bethesda assay. anti-hFVIII, antihuman factor VIII; anti-rpFVIII, antirecombinant porcine factor VIII; CSA, chromogenic substrate assay; Cyclo, cyclophosphamide; FVIII, factor VIII.