Recommendations for harmonizing definition, recording and reporting of the annual bleeding rate (ABR) in hemophilia: Communication from the ISTH SSC Subcommittee on Factor VIII, Factor IX and Rare Coagulation Disorders.".

Bleeding manifestations not only correlate with the severity of hemophilia but are also used to assess efficacy of treatment. Accurate determination of bleed events and its frequency as well as its reporting in a harmonized manner is crucial for the assessment of efficacy of therapeutic interventions. Bleeding into large joints, the most common manifestation of severe hemophilia, can be challenging to recognize especially if very mild or associated with pre-existing arthropathy. A previous ISTH SSC working group provided definitions for determination of joint and muscle bleed events in 2014, but these have not been consistently applied in clinical trials or practice. Additionally, there is wide variation in the literature with regard to reporting of aggregate bleed events including those at specific sites, differentiation between spontaneous and traumatic bleeds, and the central tendencies of data and observation period over which such data are acquired. These aspects were not covered in the previous SSC recommendations. A new SSC working group was therefore constituted to review the available literature and engage with stakeholders to prepare recommendations for recognition of bleed events, particularly into the joint, as well as their recording and reporting including terminologies and methods to be used for communication of aggregate data. Here we provide a modified definition of a joint bleed, as well as recommendations for the harmonization of the reporting of bleed events including the efficacy period and calculation of bleed rates. It is recommended that these definitions are applied in future clinical trials and practice to support comparison of novel treatments and shared decision making.