Understanding minimum and ideal factor levels for participation in physical activities by people with haemophilia: An expert elicitation exercise

The benefits of physical activity (PA) for people with haemophilia (PWH) may include improvements in joint, bone and muscle health. However, the factor VIII activity level required to avoid a bleeding episode associated with PA is unknown. Aim To elicit the opinion of clinical experts on the minimum level and ideal factor VIII activity (‘level’) required to avoid a bleeding episode during participation in different types of PA for PWH. Methods Based on the 2017 National Hemophilia Foundation PA descriptions, clinical experts estimated a minimally acceptable and an ideal factor level at which a bleed could be avoided. The uncertainty around estimates was quantified using an approach to construct a probability distribution to represent expert opinion. Results Minimum and ideal factor level increased with higher risk PA, whether or not joint morbidity was present, as did the experts' uncertainty in their estimates (ie the range between lowest and highest estimates for minimum and ideal levels). Mean minimum levels ranged from 4% to 48% for low to high risk for people without joint morbidity, and from 7% to 47% for those with joint morbidity. For ideal factor levels, corresponding figures were 9%‐52% and 12%‐64%, respectively. Conclusion To support a patient‐centric outcome, expert opinion indicates that the clinical norm of 0.01 IU/mL (1%) trough level is insufficient. It is anticipated that introducing a more targeted approach to meet the needs of patients who are increasingly physically active will benefit patients further in addition to recent treatment advances.