No Evidence for Contracting Dementia From Blood Transfusions

Beth Skwarecki

June 28, 2016

There is no evidence dementia can be transmitted through blood transfusions, according to a retrospective cohort study of Scandinavian blood donors and recipients published online June 27 in the Annals of Internal Medicine.

Alzheimer's and Parkinson's diseases, as well as amyotrophic lateral sclerosis and other neurodegenerative conditions, involve protein aggregation that propagates in a manner similar to prions. Animal experiments have shown that injecting misfolded beta-amyloid protein into the brains of rodents and primates can cause proteins to aggregate, suggesting these neurodegenerative diseases may be transmissible.

Blood transmission has not been shown to transmit these diseases, although variant Creutzfeldt-Jakob disease, caused by a prion, can be transmitted this way.

To further examine the possibility, Gustaf Edgren, MD, PhD, from the Karolinska Institutet and Karolinska University Hospital in Stockholm, Sweden, and colleagues used a database of Swedish and Danish blood transfusions going back 44 years to look for evidence that neurodegenerative diseases were being transmitted.

The databases include some transfusions dating back to 1968 in Sweden and 1981 in Denmark, and all transfusions performed in those countries since 1995 and 2003, respectively. The researchers were able to link donors and recipients in national patient registers, to see whether they were later diagnosed with Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, or dementia of any type except Creutzfeldt-Jakob disease.

For each of the 1,465,845 recipients in the study, the team considered blood transfusions in the 6 months after the person's first transfusion. A recipient was considered to be exposed if any of their donors, within that period, went on to develop dementia within the next 20 years. The median follow-up among the 1,169,475 donors was 10.4 years.

There was no association between exposure and diagnosis for dementia of any type (hazard ratio, 1.04; 95% confidence interval, 0.99 - 1.09). The investigators saw similar findings when they analyzed the risk for Alzheimer's and Parkinson's separately (hazard ratio, 0.99 and 0.94, respectively). However, only seven patients were exposed to amyotrophic lateral sclerosis, so the researchers could not draw any conclusions about this disease.

The authors also analyzed the data in a second way, looking for increased rates of dementia among all of the recipients of each donor. This should detect donors who would be able to transmit dementia without developing symptoms themselves. No link was found with this model, either (P = .72).

To test their analysis, the investigators performed the same calculations for viral hepatitis, which is known to be transmitted through blood transfusions. They found clear evidence of the link from transfusions performed before 1992 with both approaches, but no evidence for a link after 1992, when hepatitis screening was fully implemented in both countries.

The authors note that their method should have 80% power to detect the transmission of dementia if it existed, assuming an average induction time of 20 years, an infectivity rate of 5%, and an underdiagnosis rate of 70%.

The authors conclude that "although our findings do not formally exclude the possibility of neurodegenerative diseases being transmissible via transfusion, they do offer reassurance" that if transmission exists, it must either involve a latency period of more than 20 years or be extremely rare.

The authors have disclosed no relevant financial relationships.

Ann Intern Med. Published online June 27, 2016. Abstract

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