Why call the calculator BRuCe?

How does any parent choose the name their child? We like the sound of BRuCe. It is also, more or less, an acronym for BleedsRisk Calculator.

What does BRuCe do?

BRuCe can be used to calculate the absolute risk of bleeds that a child with haemophilia might be expected to experience if he participates in moderate or high risk physical activities.

Why would I want to do that?

BRuCe can be used to explore the changes in bleeds risk associated with participation in moderate and high risk physical activity in a child with haemophilia. You can use BRuCe to explore how, for example, playing soccer changes bleeds risk. This might inform decisions about whether a child with haemophilia should or should not participate in particular physical activities.

Who is BRuCe designed for?

BRuCe calculates risk of bleeds in children with haemophilia. The estimates of risk used by BRuCe are based on research conducted on children with moderate or severe Haemophilia A and Haemophilia B. The children who participated in that research were aged 4-18 years. In other respects they were quite a diverse group: some were on prophylaxis and others were not, and some had target joints and others did not. This means that BRuCe is best used to estimate absolute bleeds risk in children aged 4-18 years with moderate or severe Haemophilia A or B.

How is bleeds risk calculated?

OK, this gets a bit technical: The statistical methods used by BRuCe are new, although they are closely related to similar methods used by epidemiologists in other contexts. The algorithms are still being developed so they may change over time.

BRuCe calculates the absolute risk of bleeding (expressed in terms of the expected number of bleeds per year) using estimates of the relative risk of bleeding associated with physical activity (i.e., how much more likely a bleed is to occur in the period during or soon after a period of physical activity). The estimates of relative risk were derived from research conducted in Australia between 2009 and 2012 by Dr Carolyn Broderick and her colleagues. Estimates of relative risk are combined with person-specific information about the number of bleeds experienced in the past year and exposure to physical activity in the past year. These two sources of information (estimates of relative risk and person-specific information) are used to estimate a hypothetical person-specific baseline risk of bleeding (the number of times per year that person would experience a bleed if they did no physical activity). This in turn is used to calculate the number of bleeds that it is expected the same person would experience with a different pattern of physical activity.

Why does a change in physical activity from LAST YEAR to NEXT YEAR appear to make little difference to bleeds risk?

For some people, increasing the amount of participation in high risk physical activity only slightly increases the risk of bleeds. You might find that surprising. We did too! In fact that is one of the most important findings that has come out of the research that preceded BRuCe.

One explanation for this surprising finding is that, even though participation in moderate and high risk physical activity greatly increases the risk of a bleed in the period during and soon after physical activity, most people - even those people we would consider to very physically active - only participate in physical activity for a small proportion of time. Consequently the absolute increase in risk is small. An example might make this clearer: Imagine that a particular person with haemophilia does no physical activity at all. If that person decided to take up a new physical activity for 2 hours every week day for 6 months of the year (i.e. for an average of 5 hours per week over a year) and if that activity increased the risk of bleeds during and soon after the activity by a factor of 5, then the total risk would be increased by a factor of 5 for on average 5 hours each week. But the risk would be unchanged for the remaining 163 hours per week in which the person was not participating in physical activity. Increasing risk by a factor of 5 for 5/168 hours (less than 3% of the time) increases total risk, and therefore also the expected number of bleeds, by only 15%.

If participation in a particular physical activity makes little difference to bleeds risk, does that mean I should be able to participate in that activity without having to worry about bleeds?

Not necessarily. There are some other important considerations:

You must also consider the consequences of the bleeds. Some activities (such as boxing, rugby and high diving) may risk intracranial bleeds (bleeds in the brain). Intracranial bleeds can cause permanent serious disability or death. Even a very small increase in the risk of intracranial bleeds is undesirable. So even if the absolute increase in risk of bleeds associated with these activities is small it may nonetheless be advisable to avoid these activities altogether. 

Another consideration is that, while moderate and high risk physical activities may produce only small increases in the risk of observable bleeds in some people, the same activities may increase the risk of unobserved ("sub-clinical") bleeds. BRuCe cannot make any predictions about sub-clinical bleeds. Many haematologists believe that even though sub-clinical bleeds don't immediately cause pain and swelling repeated sub-clinical bleeds into the same joint can eventually cause joint damage. For that reason it may be advisable to avoid some physical activities even if they have little effect on the risk of observable bleeds.

BRuCe can help you estimate the risk of clinical bleeds, and estimates of the risk of clinical bleeds can be used to inform decisions about participation in physical activity. But when making decisions about participation in physical activity you need to carefully weigh up the consequences of the bleeds. A haematologist or a paediatrician or a physiotherapist who works specifically with people with haemophilia can help you make balanced decisions about whether or not to participate in particular physical activities.