Definitions in Hemophilia: Resolved and Unresolved Issues

Abstract Definitions of clinical events and end points of care are important for disease characterization as well as documentation of outcomes in clinical practice and trials. Until recently, the only definitions in hemophilia that were provided through an international scientific organization related to disease severity and levels of inhibitors. Recently, the Scientific and Standardization Committee (SSC) of the International Society on Thrombosis and Haemostasis, through its Factor VIII and IX subcommittee, published consensus definitions for several other aspects of hemophilia management, including classification of disease severity; inhibitors; bleeding (and rebleeding) into muscles and joints; target joints; different forms of factor replacement therapy; and response to therapy for joint bleeding and surgical hemostasis. These definitions should help to bring greater uniformity in the documentation of critical clinical events and laboratory data that are reported both from clinical trials as well as real-world practice. This article describes these definitions in greater detail than the SSC short report and also addresses some of the unresolved issues. Wide dissemination of these concepts and definitions and their acceptance by relevant leading scientific societies, drug regulators, industry, and patient organizations will go a long way in ensuring their acceptance and use globally.