Evidence that Parkinson’s and Alzheimer’s are Not Transmitted by Blood Transfusion

“I owe my life to blood donors. I’m forever grateful to people who donate.” Niki Taylor

“We are linked by blood, and blood is memory without language.” Joyce Carol Oates

Synopsis: Could either Parkinson’s or Alzheimer’s be communicable diseases from human blood products? A recent study shows there is no evidence for these neurodegenerative disorders to be transmitted by blood transfusion.  This observation may contradict a growing hypothesis of a prion-like pathogenesis process for Parkinson’s.  The goal of this post is to present a brief overview of blood transfusion medicine and the study that suggests Parkinson’s and Alzheimer’s are not transmitted through blood transfusion.

“The easiest thing to be in the world is you. The most difficult thing to be is what other people want you to be. Don’t let them put you in that position.” Leo Buscaglia

Brief history of transfusion medicine (derived from a lecture in my undergraduate Biology/Pathology course): Galen of Pergamon was a Greek physician-philosopher who believed in the four humors of Hippocratic medicine, which were black bile, yellow bile, phlegm, and blood. Each of the four humors corresponded to one of the four traditional personality types/traits. Galen’s theories influenced Western medical science for many years, where blood-letting was even used medically to release a body of a bad humor (see the 2 images on the left side of the figure below).

Galen’s theory of blood circulation physiology lasted until 1628 when William Harvey showed that the heart acts as a pump to circulate the blood. By this time, everyone was aware of the life-giving qualities of blood. In the 1600’s, physician-scientists developed techniques to isolate dog veins, which led them to experiment with the transfusion from dog to dog. Jean-Baptiste Denys carried out the first transfusion of animal to human. The patient complained of “a very great heat along his arm”. Antoine Mauroy had received calves’ blood, he had pain in the transfused arm, vomiting, kidney dysfunction, and pressure in the chest. The next day he passed black urine; he had all of the “classic symptoms” of a hemolytic transfusion reaction. Sadly, Mauroy was re-transfused the next day and died, which resulted in Denys being charged with murder (see the 2 images on the middle of the figure below).   Jump ahead to the 1800’s, and Dr. James Blundell further describes human-to-human blood transfusion studies in a publication in the medical journal Lancet.

“And so I conclude that blood lives and is nourished of itself and in no way depends on any other part of the body as being prior to it or more excellent… So that from this we may perceive the causes not only of life in general… but also of longer or shorter life, of sleeping and waking, of skill, of strength and so forth.” William Harvey

In 1900, Karl Landsteiner performed a series of experiments with 22 colleagues in which the red blood cells of each individual were mixed with the serum of each of the others. From agglutination studies, he found three groups, which he named A, B and C. Landsteiner received the Nobel Prize in Physiology or Medicine in 1930 for discovering blood groups and the beginning of transfusion medicine (see the 2 images on the right side of the figure below).

“I have recently observed and stated that the serum of normal people is capable of clumping the red cells of other healthy individuals… As commonly expressed, it can be said that in these cases at least two different kinds of agglutinins exist, one kind in A, the other in B, both together in C. The cells are naturally insensitive to the agglutinins in their own serum.” Karl Landsteiner


Blood facts and statistics in the USA (for the full set of lists, please click here): (a) every two seconds someone in the U.S. needs blood,  ~36,000 units of red blood cells are needed every day in the U.S., and  ~7,000 units of platelets and 10,000 units of plasma are needed daily in the U.S., respectively; (b) the yearly U.S. blood supply is through collection of 13.6 million units of whole blood and red blood cells from 6.8 million donors; (c) blood donation is a safe process that is a simple four-step process that consists of registration, medical history and mini-physical, donation and refreshments; (d) the average adult has about 10 pints of blood in their body with ~1 pint given during a donation; and (e) there are four types of transfusable products obtained from blood: red cells, platelets, plasma and cryoprecipitate, and a single donation can potentially help more than one patient.


“Blood is a very special juice.” Johann Wolfgang von Goethe

Is there a risk of getting either Parkinson’s disease or Alzheimer’s disease from blood products?  Short-answer, no. This conclusion was reported by  Edgren, G., et al. (2016). “Transmission of neurodegenerative disorders through blood transfusion: A cohort study.” Annals of Internal Medicine 165(5): 316-324 (click here to view paper).  This is a retrospective cohort study, which means a scientific study of a group of people (cohort) that share a common exposure factor (here it a blood transfusion) to determine its influence on getting a disease (here it would be a neurodegenerative disease such as Parkinson’s  or Alzheimer’s), and then comparing this group of people to individuals not exposed to this situation/factor.

The study was based on >40 000 patients from a Swedish-Danish transfusion database who had received blood between 1968 and 2012 from donors who were later diagnosed with Parkinson’s, Alzheimer’s or dementia.  The comparison was then done with more than 1.4 million patients who never received blood from donors who subsequently received a diagnosis of a neurodegenerative disorder (Parkinson’s, Alzheimer’s or dementia). They found 2.9% of this group of patients had received a blood product from a donor later diagnosed with a neurodegenerative disorder.  This group of  patients who received blood from donors who were later diagnosed with a neurodegenerative disorder were followed for many years (up to 44 years), and they were matched for sex, age, and time since first transfusion (among some of the features compared/studied).

A big strength of this study was a rigorous statistical analysis of these patients that revealed there was no evidence of transmission of any of these neurodegenerative diseases. If you like statistics keep reading because they calculated a hazard ratio of 1.04 (95% CI, 0.99 to 1.09) for dementia in recipients of blood from donors with dementia versus recipients of blood from healthy donors, and they found for Parkinson’s a hazard ratio of 0.94 (95% CI, 0.78-1.14) and for Alzheimer’s a hazard ratio of 0.99 (95% CI, 0.85-1.15), neither of which were significant. The conclusion from these results suggest that there is no evidence that either Parkinson’s or Alzheimer’s is being transmitted through blood transfusion.

“The blood is the life!” Bram Stoker

Neurodegenerative disorders and prions:  The above study somewhat complicates the growing notion that α-synuclein acts as a prion-like substance to contribute to the development of Parkinson’s.  What are prions? Prions are proteins that take-on alternate shapes to cause disease. Prions were discovered while studying the cause of rare neurodegenerative diseases of animals and humans called scrapie and Creutzfeldt–Jakob disease, respectively.  Importantly, variant Creutzfeldt-Jakob disease (vCJD) may be transmissible by blood (click here to learn more) and blood products (click here); however, as found in the United Kingdom, most cases of vCJD have occurred due to increased potential exposure to contaminated beef in the diet.  Like α-synuclein in Parkinson’s, the prion-like substance in Alzheimer’s is a misfolded fragment of amyloid beta (Aβ) protein. Aβ fragments are prion-like in their manner of neuronal cell transmission.  A future post will describe in further detail the prion hypothesis for Parkinson’s disease (aggregates of α-synuclein) and Alzheimer’s  disease (aggregates of Aβ protein fragments).  The prion hypothesis of Parkinson’s and Alzheimer’s suggests these aggregated proteins are directly toxic to healthy neurons as documented in other prion disorders.

“It will have blood, they say; blood will have blood.” William Shakespeare

Blood donation and Parkinson’s, a personal perspective: The paper from Edgren et al. says that it is safe to donate blood even if you have Parkinson’s.  Their results tell me it is okay to continue to donate my blood to the American Red Cross.  This is especially important since I had been donating blood during the window-of-time where I had Parkinson’s before the actual diagnosis.  Good news!


 “Let ourselves be seen, deeply seen, vulnerably seen, to love with our whole hearts, even though there’s no guarantee… to practice gratitude and joy in those moments of terror… to say ‘I’m just so grateful because to feel this vulnerable means I’m alive’… to believe that we’re enough. Because when we work from a place, I believe, that says, ‘I’m enough’, then we stop screaming and start listening, we’re kinder and gentler to the people around us, and we’re kinder and gentler to ourselves.” Brené Brown

Cover photo credit:  https://c2.staticflickr.com/8/7156/6782892659_a4bec2c07d_b.jpg



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