Estimation of transient increases in bleeding risk associated with physical activity in children with haemophilia

The study will be a case-crossover study nested within a prospective cohort study. Children with moderate or severe haemophilia A or B, recruited from two paediatric haematology departments in Australia, will participate in the study. The child, or the child's parent or guardian, will report bleeding episodes experienced over a 12-month period. Following a bleeding episode, the participant will be interviewed by telephone about exposures to physical activity in the case period (8 hours before the bleed) and 2 control periods (an 8 hour period at the same time on the day preceding the bleed and an 8 hour period two days preceding the bleed). Conditional logistic regression will be used to estimate the risk of participating in vigorous physical activity from measures of exposure to physical activity in the case and control periods.This case-control study will provide estimates of the risk of participation in vigorous physical activity in children with haemophilia.Haemophilia affects 1 in 7,000 males in Australia.[1] Clinically, haemophilia is characterised by bleeds, most often into muscles or joints. Some children with hemophilia develop "target joints" when multiple bleeds into the same joint lead to destruction of the joint surfaces (haemophilic arthropathy).Over the past decade there has been a move to treat children with moderate and severe haemophilia prophylactically. Typically a child may be given two to three intravenous injections of recombinant factor VIII or IX each week. Injections may be timed to precede vigorous physical activity because vigorous physical activity is thought to elevate the risk of bleeding episodes. Prophylactic clotting factor injections reduce the number of bleeding episodes, but many children with moderate and severe haemophilia still experience bleeding episodes several times a year.Although it is widely believed that vigorous physical activity can increase the risk of bleeds, the magnitude of the increase in risk is not known. Accu