People who receive blood from a donor who later experiences more than one intracerebral haemorrhage 鈥� blood vessels rupturing in their brain 鈥� have a heightened risk of experiencing a brain haemorrhage themselves. Although the risk is very small, it suggests that intracerebral haemorrhages may have a transmissible cause.
These brain bleeds are commonly triggered by the accumulation of proteins called amyloid in the walls of the brain鈥檚 blood vessels. A in humans have hinted that through medical procedures. So, at the Karolinska Institute in Sweden and his colleagues analysed intracerebral haemorrhage rates among people who received blood transfusions. They used the condition as a proxy for amyloid build-up since the latter is rarely diagnosed, he says.
Utilizing nationwide health records, they collected data on almost 760,000 people from Sweden and nearly 330,000 people from Denmark who underwent a blood transfusion between the late 1960s and 2017. At the time of transfusion, the participants were between 5 and 80 years old and none had a history of intracerebral haemorrhage, previous blood transfusions or brain tumours. Edgren and his colleagues excluded people whose blood donor had experienced an intracerebral haemorrhage before donation.
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The risk of experiencing a brain bleed after a transfusion is always low. However, the researchers found that the relative risk was more than twice as high for people who received transfusions from donors who later had at least two intracerebral haemorrhages than recipients whose donors didn鈥檛 experience a brain bleed later. This suggests that an underlying cause of intracerebral haemorrhage 鈥� potentially amyloid 鈥� may be transmitted through blood.
The team also found that receiving blood from someone who experienced only one intracerebral haemorrhage later in life didn鈥檛 increase the risk of brain bleed. The researchers noted that this could be because haemorrhages due to amyloid are more likely to recur than blood vessel ruptures from other causes.
Amyloid build-up is also common in dementia-related conditions like Alzheimer鈥檚 disease, says Edgren. This may explain why they found that a recipient鈥檚 risk of a brain bleed more than doubled if their transfusion donor later experienced only a single intracerebral haemorrhage but also developed dementia.
鈥淭here are many different causes of intracerebral haemorrhage,鈥� says at Stanford University in California. 鈥淪o, I don鈥檛 think we can make any conclusions about whether the haemorrhages that [the researchers] are seeing in these patients who got transfusions are due to [amyloid].鈥�
Edgren agrees. He and his team are now gathering samples from stored blood donations in Denmark to test them for amyloid proteins. They are also attempting to procure brain scans from participants who developed haemorrhages to see if they were caused by amyloid build-up. Both of these efforts will help determine whether the increased risk of intracerebral haemorrhage in this study is due to amyloid transmission. If so, that would yield clues about the cause of amyloid build-up and potentially even Alzheimer鈥檚 disease, he says.
In the meantime, Edgren stresses that the absolute risk of intracerebral brain haemorrhage from a blood transfusion is incredibly small 鈥� about 2 per cent over a 30-year period. 鈥淕etting a transfusion is incredibly safe,鈥� he says. 鈥淭his is not something a patient who needs a transfusion should worry about.鈥�
JAMA
