Factor VIII Inhibitor Assays: Methodology, Shortcomings, and Challenges

ABSTRACT Development of inhibitory antibodies against factor VIII is a serious complication in the treatment of hemophilia patients, as theseantibodies inactivate factor VIII, resulting in an increased bleeding tendency and morbidity. The clinical manifestation of inhibitors has to beanalyzed by objective laboratory tests to specify the exact nature of the inhibitor. Here, the inhibitor assays, especially the Bethesda assay andthe Nijmegen assay, are discussed including their methodological shortcomings. This paper also discusses the epitope specificity of theinhibitor assays and the methods to investigate the specificity of inhibitors against factor VIII concentrates that may contribute to improvethe treatment of hemophilia A patients with inhibitors. Finally, the use and limitations of overall clotting assays, such as clot wave formanalysis, thromboelastography, and thrombin generation assay, in the management of hemophilia A patients with inhibitors are discussed.Keywords: hemophilia A, factor VIII inhibitors, Nijmegen assay, Bethesda assay, epitope specificityCorrespondence: B Verbruggen, Laboratory of Hematology, Department of Laboratory Medicine, Radboud University Nijmegen MedicalCenter, PO Box 9101, 6500 HB Nijmegen, The Netherlands. Tel: (31)-243614796; e-mail: H.Verbruggen@chl.umcn.nl