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Getting Closer to a Blood Test for Alzheimer’s Disease?

Posted on by Dr. Francis Collins

Blood Test

As research on Alzheimer’s disease (AD) advances, a desperate need remains for an easy blood test to help diagnose the condition as early as possible. Ideally, such a test could also distinguish AD from other forms of dementia that produce similar symptoms. As published recently in Nature Medicine, an NIH-funded research team has designed a simple blood test that is on course to meet these criteria [1].

The latest work builds on a large body of work showing that one secret to predicting a person’s cognitive decline and treatment response in AD lies in a protein called tau. Using the powerful, but expensive, approach of PET scan imaging, we know that tau builds up in the brain as Alzheimer’s disease progresses. We also know that some tau spills from the brain into the bloodstream.

The trouble is that the circulating tau protein breaks down far too quickly for a blood test to offer a reliable measure of what’s happening in a person’s brain. A few years ago, researchers discovered a possible solution: test for blood levels of a slightly different and more stable version of the protein called pTau181 [2]. (The “p” in its name comes from the addition of phosphorus in a particular part of the protein’s structure.)

In the latest study, researchers in the lab of Adam Boxer, University of California, San Francisco, followed up further on this compelling lead. Boxer’s team measured pTau181 levels in blood samples from 362 people between the ages of 58 and 70. Those samples included 56 people with an Alzheimer’s diagnosis, along with 47 people with mild cognitive impairment and 69 healthy controls.

The researchers also included another 190 people diagnosed with frontotemporal lobar degeneration (FTLD). It is a relatively rare form of dementia that leads to a gradual decline in behavior, language, and movement, often in connection with a buildup of tau in the brain.

The study found that levels of pTau181 were roughly 3.5-times higher in the blood of people with AD compared to people without AD. Those with mild cognitive impairment due to underlying AD also showed an intermediate increase in blood levels of pTau181.

Importantly, people with FLTD had normal blood levels of pTau181. As a result, the blood test could reliably distinguish between a person with AD and a person with FLTD. That’s important because, while FLTD is a relatively rare condition, its prevalence is similar to AD in people under the age of 65. But both conditions have similar symptoms, making it often challenging to distinguish them.

The findings add to evidence that the new blood test can help in diagnosing AD and in distinguishing it from other neurodegenerative conditions. In fact, it does so with an accuracy that often rivals more expensive PET scans and more invasive cerebrospinal fluid tests, which are now the only reliable ways to measure tau.

There’s still plenty of work to do before this blood test is ready for a doctor’s office. But these initial findings are very promising in helping to simplify the diagnosis of this devastating condition that now affects an estimated 5.5 million Americans [3].


[1] Diagnostic value of plasma phosphorylated tau181 in Alzheimer’s disease and frontotemporal lobar degeneration. Thijssen EH, La Joie R, Wolf A, Strom A, Wang P, Iaccarino L, Bourakova V, Cobigo Y, Heuer H, Spina S, VandeVrede L, Chai X, Proctor NK, Airey DC, Shcherbinin S, Duggan Evans C, Sims JR, Zetterberg H, Blennow K, Karydas AM, Teunissen CE, Kramer JH, Grinberg LT, Seeley WW, Rosen H, Boeve BF, Miller BL, Rabinovici GD, Dage JL, Rojas JC, Boxer AL; Advancing Research and Treatment for Frontotemporal Lobar Degeneration (ARTFL) investigators. Nat Med. 2020 Mar 2.

[2] Plasma phospho-tau181 increases with Alzheimer’s disease clinical severity and is associated with tau- and amyloid-positron emission tomography. Mielke MM, Hagen CE, Xu J, Chai X, Vemuri P, Lowe VJ, Airey DC, Knopman DS, Roberts RO, Machulda MM, Jack CR Jr, Petersen RC, Dage JL. Alzheimers Dement. 2018 Aug;14(8):989-997.

[3] Alzheimer’s Disease Fact Sheet. National Institute on Aging, May 22, 2019.


Alzheimer’s Disease & Related Dementias (National Institute on Aging/NIH)

What Are Frontotemporal Disorders? (NIA)

Accelerating Medicines Partnership: Alzheimer’s Disease (NIH)

Adam Boxer (University of California, San Francisco)

NIH Support: National Institute on Aging; National Institute of Neurological Disorders and Stroke; National Center for Advancing Translational Sciences


  • Mike Hasan says:

    Thanks for such an informative and well written article.

  • Philippe Pilon says:

    Hello NIH team,

    Wow that is awesome ! What are the predispose symptoms for AD and FLTD ? What does a person, that is not diagnose yet, feel within herself just before, boom you are diagnose !

  • Ivan Miller says:

    The article mentioned “plenty of work to do” before this test is available to doctors. Just how long is this estimated period of time in years. I understand unanticipated problems may occur, adding more time before a finished product is released to the medical community..

  • DR. SAUMYA PANDEY, PH.D. says:

    An innovative therapeutically significant patient-centric snapshot in the complex Alzheimer;s Disease field!
    Tau-protein misfolding, post-translational aberrant modifications, conformational changes in the oligomers/subunits in Tau proteins in borderline to clinically symptomatic AD and associated neurological disease-patients, including traumatic brain-tumors/glioblastomas, acoustic neurological disorders, etc. warrant future scientific investigations with high-throughput transcriptomics, proteomics and metabolomics approaches coupled with pharmacological strategies for rationale drug design and pharmacogenetics/genomics case-control multicentric gene-polymorphism based epidemiology studies for eventual Tau-protein-related predictive biomarkers for early identification and stratification of AD-susceptible populations of genetically heterogeneous populations worldwide, including American, Asian Indian, etc. cohorts.
    Overall, the blood-test protocol should be further investigated in replicative studies with pooled population-subsets of AD-positive cases and healthy, disease-free controls for deducing statistically significant predictive outcomes in cost-effective AD clinical management and surveillance of adverse effects following blood-tests in AD-symptomatic patients with subgroup stratification of A/B/O Rh+ vs ABO Rh- patient-subsets.
    Good practice clinical research with scientific integrity and written informed consent of study-subjects in multicentric prospective, cross-sectional large sample-size based studies would be immensely beneficial in drawing definitive conclusions in Tau-mediated AD-clinical management in ethnically disparate populations worldwide.

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