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A New Blood Test May Soon Detect Alzheimer’s Disease

Monday, October 19th, 2020

Currently, Alzheimer’s diagnoses are made mostly with clinical assessments of the person’s cognitive, physical, mental, and functional health, often assisted by interviews with family members and caregivers. Sometimes the diagnoses may be uncertain due to confusions around distinguishing Alzheimer’s from other dementias and physical conditions that involve cognitive impairment. The more accurate diagnostic tests involving brain scans and spinal taps are expensive and invasive. Else, the most definitive diagnostic method is a brain autopsy post-mortem. Thus, the dementia community are understandably excited by recent research showing promise for a blood test measuring phospho-tau217 (p-tau217) in detecting Alzheimer’s Disease[1].

P-tau217 is a major component of the tau tangles seen in the brains of people with Alzheimer’s disease[2]. The cross-sectional study evaluated the p-tau217 blood test in 1402 participants across a trio of well-known cohorts.

  1. The first cohort comprised 81 participants from a brain donation program in Arizona. The donors participated in cognitive assessments and provided blood samples in their last years of life, and their brains were then studied after they died. The study found that the blood test discriminated between brain donors with and without a post-mortem diagnosis of “intermediate or high likelihood Alzheimer’s” with 89% accuracy; and those with and without a diagnosis of “high likelihood Alzheimer’s” with 98% accuracy.
  2. The second cohort involved 699 Swedes who participated in a range of cognitive, brain imaging, cerebrospinal fluid, and blood-based assessments. The study found that the blood test was 96 percent accurate in determining whether people with dementia had Alzheimer’s rather than other neurodegenerative disorders. This performance was comparable to the accuracy rates of PET scans and spinal taps, and better than several other blood tests and MRI measurements.
  3. Finally, the team tested p-tau217 in 622 members of the world’s largest known family with genetic early-onset Alzheimer’s. The test was essentially found to identify who would develop the disease 20 years before dementia symptoms would surface. In this extended family in Colombia, some members have a mutation that causes cognitive impairment beginning in their mid-40s. The test could distinguish between those with and without the mutation in people as young as 25.

A gateway to more affordable and accessible research

A blood test like this could accelerate the search for new therapies by making it faster and cheaper to screen participants for clinical trials. Detecting tau could also be valuable for predicting how quickly a person’s cognitive abilities will decline. Unlike amyloid plaques – another common biomarker for Alzheimer’s – tau tends to increase as dementia worsens.

Increased Ethical Considerations

However, the ability to diagnose Alzheimer’s with a quick blood test could intensify emotional dilemmas for people deciding whether they want to know if they have a condition that does not yet have a cure or treatment. There is still some work to do to develop the research grade blood test to a clinical grade standard – not least it would first need to be replicated in clinical trials with more ethnically diverse populations. Nonetheless, the findings offer important hope for a quick diagnostic test for Alzheimer’s.