Could Blood Transfusions Transmit Alzheimer's Disease?

Alzheimer's and the possibility of infectious transmission

Alzheimer's has traditionally been understood as a sporadic disease, shaped by influences including age, genetics and lifestyle. Yet scientists do not believe this is the disease's only possible origin.

More recently, researchers have proposed that Alzheimer's could also spread through infection, potentially being transmitted like a pathogen before eventually developing into the disease.

A new report in The Lancet examines evidence relating to one part of this hypothesis: whether damaging amyloid-beta proteins linked with Alzheimer's could potentially be passed on through blood transfusions.

"Blood transfusions are important and save many lives," says University College London neurologist John Collinge.

"However, to ensure that they are as safe as they can possibly be, it's important that we thoroughly investigate any potential risks."

Evidence for amyloid-beta transmission through medical procedures

A 2015 study offered the first real-world evidence that amyloid pathology could be transferred between people during medical procedures. Further research in 2016 identified additional evidence for the same possibility.

Other research published in the intervening years has added further support. A 2018 paper indicated that contaminated surgical instruments could pass Alzheimer's proteins from one patient to another, perhaps in a process resembling the way infectious prions cause healthy proteins to misfold into harmful forms.

Blood transfusions, CAA and Alzheimer's risk

For the potential risks associated with transfusions, an important development came in 2023. A large population study in Denmark and Sweden found that people given transfusions from donors who later experienced intracerebral haemorrhages were themselves more likely to suffer repeated brain bleeds years later.

This matters because spontaneous brain haemorrhages are a defining symptom of cerebral amyloid angiopathy (CAA). Although CAA is distinct from Alzheimer's, it is also linked to amyloid-beta proteins.

Collinge and his colleagues consider the "most biologically plausible explanation" to be that donors' blood contained early amyloid-beta seeds that had not yet progressed into CAA, and that these were passed to recipients during transfusion.

That explanation is not certain, and the researchers are careful not to make claims beyond the available evidence.

Blood transfusions could potentially transmit the seeds of Alzheimer's disease, researchers suggest. (Sezeryadigar/Getty Images Signature/Canva)

However, they maintain that enough is known about the possible danger to begin considering protections, should blood-borne transmission of Alzheimer's pathology prove to be more than a theoretical concern.

"The transmission of amyloid-beta pathology via transfused blood and blood products is a justifiable concern," the researchers write in their paper.

"We need to acknowledge that we do not have sufficient information to quantify the extent of the problem or the technologies that are needed to address key questions."

The team first calls for large epidemiological studies, such as the Scandinavian study, which included more than 1 million people. These could investigate more fully whether transfusions transfer something other than blood alone.

Further precautions might include closer follow-up of patients with higher risk, such as those requiring repeated transfusions. The researchers also suggest a system for determining whether blood biomarkers for Alzheimer's could identify donors who may carry amyloid-beta pathology.

Calls for caution and further research

Although the risks remain largely theoretical for now, the researchers argue that the consequences of failing to prepare are already well understood.

The UK Infected Blood Inquiry, published in 2024, investigated the UK infected blood scandal. Contaminated blood may have infected more than 30,000 patients between the 1970s and 1990s, in what has been described as "the worst treatment disaster in the history of the National Health Service".

"The Infected Blood Inquiry provides a cautionary tale in waiting for absolute certainty before making decisions on patient safety," Collinge says.

"We also think it's important to be open and transparent about possible risks of amyloid-beta transmission, so that we can proactively mitigate any potential risk to patients."

Related: Prion-Like Brain Damage Can Occur Without Infectious Prions, Study Finds

Experts agree that the known dangers are currently low, but say more must be learned about what may be occurring while preserving public trust in the safety of blood transfusions.

"What this review does is identify an important gap in our knowledge," says Susan Kohlhaas, Executive Director of Research and Partnerships at Alzheimer's Research UK, who was not involved in the paper.

"The authors make the case for specific research to establish whether transmission through blood is occurring, who might be most at risk, and whether measures are needed to reduce that risk.

"At present, we simply don't have enough evidence to answer those questions, which is why this is important, and more research is needed."

The findings appear in The Lancet.

This article was fact-checked and edited by Michael Irving. Although we take pride in our process, we are only human. If you notice an error, please let us know.