A Multicenter Study to Describe the Immunogenic Epitope(s) of Factor VIII in Previously Treated Patients With Congenital Hemophilia A Who Develop De Novo Factor VIII Inhibitors While Receiving Factor VIII Infusion Therapy.

This investigation will utilize a systematic determination of anti-FVIII antibody specificity in PTPs (> 50 ED) with hemophilia A who have developed inhibitors in response to treatment with any FVIII product(s). A group of patients with hemophilia A, who have no evidence of current or prior FVIII inhibitor will be included for comparison. The objective of this study is to describe the patterns of antibodies and associated epitopes in the study population.