Variation in inhibitor reactivity in acquired haemophilia A with differentconcentrates

Acquired haemophilia A due to the development of auto-antibodies directed a gainst factor VIII (FVIII) is a rare disorder that may result in serious ha emorrhagic episodes. Although in many cases no associated underlying disord ers are apparent, the condition has been reported in association with autoi mmune disorders, haematological malignancies, treatment with certain drugs and pregnancy. The reaction kinetics of auto-antibodies to FVIII differ fro m those observed with allo-antibodies in congenital haemophilia. Previous s tudies in congenital haemophilia have raised the possibility that inhibitor y antibodies vary in their reactivity with the factor VIII molecules in dif ferent concentrates used for treatment. However, the interaction of FVIII i n concentrates and inhibitors in acquired haemophilia has never been previo usly studied. In this study, the effect of different FVIII concentrates was studied on neutralization in vitro by performing inhibitor titres using th e New Oxford inhibitor assay method. The inhibitor titre in eight patients with acquired haemophilia A was assay ed against five commercially available FVIII concentrates of varying purity . The intermediate purity concentrate 8Y and the high purity concentrate th at contains normal amounts of von Willebrand's Factor (vWF) (Alphanate) gav e lower titres than the high purity concentrates with low (Monoclate-P) or no (Kogenate) von Willebrand content. All but one antibody had very low rea ctivity with porcine FVIII. Further work will be required to establish whet her concentrates manifesting a low level of in vitro reactivity with the in hibitor have a better haemostatic effect in vivo.