Lancet Review Suggests Alzheimer's Proteins May Be Transmitted Via Blood Transfusions

A new review published in The Lancet has raised the scientific possibility that amyloid-beta—a protein central to Alzheimer's disease and cerebral amyloid angiopathy (CAA)—could be transmitted through blood transfusions under rare circumstances. The review, led by researchers at University College London (UCL), does not conclude that Alzheimer's is contagious or that the current blood supply is unsafe. Instead, it calls for proactive research and the development of new screening tools to investigate a theoretical risk before it becomes a public health issue. The authors emphasize that their goal is to ensure that uncertainty does not prevent vital research, while simultaneously avoiding unwarranted alarm over a treatment that remains absolutely essential to modern healthcare.[1][2]

Millions of life-saving blood transfusions are performed globally each year for patients undergoing surgery, trauma care, and cancer treatment. Current blood-safety systems are highly effective at screening for infectious agents like HIV and hepatitis, preventing incompatible transfusions, and reducing other known hazards. However, the concern discussed in the new paper is fundamentally different. Amyloid-beta is not a conventional virus or bacterium; it is a protein fragment that can misfold, accumulate in tissue, and potentially act as a "seed" for further abnormal protein aggregation. Whether such material can survive standard blood processing techniques and subsequently produce disease in a recipient remains uncertain, prompting the call for a systematic assessment of the potential risk.[1][3]

To understand the theoretical risk, it is necessary to examine how amyloid-beta operates within the body. Amyloid-beta is a small protein fragment generated when a larger membrane protein, known as amyloid precursor protein, is metabolized. In Alzheimer's disease, these fragments can accumulate in the brain as extracellular plaques, disrupting neural function and leading to cognitive decline. In cerebral amyloid angiopathy (CAA), the deposits form primarily within the walls of small and medium-sized blood vessels in the brain. These accumulations weaken the structural integrity of the vessels, making them increasingly brittle and susceptible to microbleeds or larger, potentially fatal intracerebral hemorrhages. Because these proteins circulate in the bloodstream before depositing in the brain, the theoretical pathway for transfusion transmission is biologically plausible.[1][2]

The UCL team's inquiry was heavily influenced by a large Scandinavian epidemiological study published in 2023. That retrospective study tracked over a million patients in Sweden and Denmark, revealing that individuals who received red blood cell transfusions from donors who later developed multiple spontaneous brain hemorrhages—a clinical marker often associated with CAA—faced a significantly higher risk of experiencing similar hemorrhages themselves. While the study was purely observational and could only identify an association rather than prove causation, the findings provided a compelling rationale for examining the issue more closely. The data suggested that a transfusion-transmissible agent might be associated with specific types of spontaneous intracerebral hemorrhage.[1][2]

This concern is further grounded in historical medical cases where amyloid-beta was inadvertently transmitted through now-discontinued procedures. In recent years, researchers have identified patients who developed iatrogenic, or medically acquired, Alzheimer's disease and CAA after receiving childhood treatments with cadaver-derived human growth hormone or dura mater grafts. Those specific treatments were halted in the 1980s and 1990s after they were found to transmit the prion proteins responsible for Creutzfeldt-Jakob disease. Subsequent autopsies and clinical evaluations revealed that the contaminated hormone preparations also carried amyloid-beta seeds, demonstrating that the pathology can indeed be transferred from person to person under exceptional, direct-exposure circumstances.[1][2]

Despite these historical precedents, experts are quick to emphasize that receiving a routine intravenous blood transfusion is vastly different from being injected with brain-derived tissue extracts. The central scientific question is not whether Alzheimer's disease is contagious in everyday life—it is not—but whether specific protein assemblies could occasionally be transferred through contemporary medical materials and later seed pathology in susceptible individuals. Independent experts reviewing the Lancet paper have stressed that the risk through blood transfusion, if it exists at all, is likely to be exceedingly small. The review primarily serves to identify an important gap in current medical knowledge rather than to announce a newly discovered crisis.[1]

Public health officials and blood transfusion services are now faced with a complex challenge: balancing the need for rigorous scientific investigation with the imperative to maintain public confidence in a critical medical procedure. Researchers are urging the development of feasible, accurate screening assays to detect amyloid-beta in blood products, as current technologies are not yet equipped to routinely screen for these specific protein assemblies at scale. Monitoring patients who have received blood transfusions over a much longer period could also help assess any long-term risk and provide the longitudinal data necessary to make informed regulatory decisions. Until those tools are developed, quantifying the exact extent of the problem remains impossible.[1][3]

In the meantime, the medical consensus remains unequivocal: patients who require blood transfusions should continue to receive them without hesitation. The known, immediate risk of refusing a necessary transfusion during surgery, trauma care, or severe anemia treatment far outweighs the theoretical and currently unproven risk of amyloid-beta transmission. Blood transfusions continue to save millions of lives across the world each year, and strict protocols are already in place to prevent the transmission of known blood-borne diseases. As researchers work to clarify the science and develop potential new safety measures, the overarching message from both the study authors and independent observers is one of reassurance and continued reliance on established, life-saving medical protocols.[1][3]