Factors Influencing Sport‐Induced Bleeding in Patients With Haemophilia Without Inhibitors: A Single Centre Retrospective Study of People Born in the 2000s

Haemophilia is a rare bleeding disorder that mainly affects boys and is caused by a lack of certain proteins (factor VIII or IX) that aid blood clotting. In the past, PwH were often told to avoid exercise because even normal activities could cause serious bleeding. However, modern treatments that prevent bleeding episodes (prophylaxis) enable PwH to participate in sports. In this study, we examined sports-related bleeding in 23 Japanese boys with haemophilia born between 2000 and 2009 to determine risk factors for bleeding. The findings showed that how often the boys played sports-particularly more than three times per week-was a stronger predictor of bleeding than how severe haemophilia was in our cohort. Regardless of sports type, most bleeding episodes happened during junior high school years, when physical growth, new sports participation, and intense physical activity are common. In our cohort of individuals with haemophilia, engaging in sports at least three times per week was associated with an increased risk of SIB, highlighting the importance of tailoring treatment plans to individual activity patterns.