In the U.S., about 1 in 9 people (10.8%) age 65 and older have Alzheimer’s disease – roughly 6.7 million Americans. (1) That number is expected to grow to 13.8 million by 2060, unless there are some significant breakthroughs to improve early detection or at least slow the progression of the disease.
Being diagnosed with Alzheimer’s is both emotionally devastating and costly. Multiple diagnostic tests and evaluations are needed for confirmation; those who don’t have access to a health facility or the money to fund the testing cannot get a diagnosis.
For so many diseases, blood work is done to determine whether the disease is present, understand its severity, and/or monitor progression or healing. This has not been the case with Alzheimer’s. Until recently, there were no accurate or reliable blood tests available. This has often led to early signs being ignored or put down to old age – until more severe symptoms appear (often years later), at which point it’s too late for any preventative or delaying measures.
What kinds of tests are being used for diagnosing Alzheimer’s disease?
Currently, there is no single test that can determine whether a person has Alzheimer’s. (2) Furthermore, when someone is not displaying any severe symptoms, diagnosis is extremely difficult. When there are signs, it typically isn’t clear whether they’re due to normal aging or something more serious. By the time the disease has progressed to the point that symptoms become apparent, approximately 60% of the patient’s neurons have probably been lost! (3)
When symptoms appear, doctors may take their patients through a battery of physical, neurological, cognitive, and behavioral assessments in addition to brain imaging, such as MRI (magnetic resonance imaging) or PET (positron emission tomography) scans.
Physicians can also use a cerebrospinal fluid (CSF) test (otherwise known as a lumbar puncture), which can be uncomfortable and invasive. This is used to determine whether tau or amyloid-beta markers can be detected in the CSF, as this may reflect changes happening in the brain (especially if Alzheimer’s disease is present).
Unfortunately, some current tests can be uncomfortable, time-consuming, and costly for the patient. After all that, some results are still open to interpretation.
Blood Tests: A New Hope for Early Detection?
Until recently, no blood test has been available for diagnosing Alzheimer’s disease, but some have been developed to measure various biomarkers. They’re being used in research settings and, more recently, in some clinical settings around the world. In the US, there’s even a blood test that can be ordered online.
But why has it taken so long to get to this point? Simply put, dementia is a complex condition.
Dementia is an umbrella term for a variety of diseases, including frontotemporal dementia, Lewy body dementia, vascular dementia, and Alzheimer’s disease. Often an older person may have mixed pathologies (more than one type of dementia at the same time) as well as other chronic health conditions. Measuring just one aspect, like traces of amyloid-beta or tau protein, may mean missing the signs of other forms of dementia.
What are these blood tests measuring?
The abnormal buildup of amyloid-beta and tau proteins is characteristic of Alzheimer’s disease. Researchers have identified ways to detect markers in the blood that indicate the presence of these proteins even before symptoms appear. The big challenge with current blood tests is the possibility of false positives, which could have a significant impact on the patient.
There are at least two reasons for false positives. First, a person may have elevated levels of markers for amyloid-beta and tau due to other problems, such as kidney disease. Also, some people with amyloid-beta buildup will continue to have normal cognitive function. A further concern is that these blood tests measure only amyloid-beta and tau proteins, which are not found in vascular or Lewy body dementia. Someone who does not test positive for Alzheimer’s may have another form of dementia.
So whilst these blood tests are a significant first step to making an earlier diagnosis, there are still some challenges. They must be used in conjunction with the current battery of assessments.
An Exciting Time
No doubt, this is an exciting time in the diagnosis and treatment of neurodegenerative diseases such as Alzheimer’s.
Researchers are already pursuing other potential markers that will overcome the challenges of current blood tests. No doubt, this will advance early detection and therapeutic interventions. It will also pave the way to make testing more accessible and affordable to many more people, including those who have been excluded or unwilling to undergo the arduous, expensive, and time-consuming process that is currently required.
It’s about time older adults get access to tests they can feel comfortable agreeing to and which give them the ability to get diagnosed – and therefore treated – earlier.
References
1. (2023), 2023 Alzheimer’s disease facts and figures. Alzheimer’s Dement., 19: 1598-1695. https://doi.org/10.1002/alz.13016 2. Medical Tests for Diagnosing Alzheimer’s – https://www.alz.org/alzheimers-dementia/diagnosis/medical_tests
3. Pollard C, Aston K, Emery BR, Hill J and Jenkins T (2023) Detection of neuron-derived cfDNA in blood plasma: a new diagnostic approach for neurodegenerative conditions. Front. Neurol. 14:1272960. doi: 10.3389/fneur.2023.1272960
4. Resonant Publishes Groundbreaking Alzheimer’s Disease Research With the Potential to Revolutionize Neurodegenerative Diagnostics https://www.prnewswire.com/news-releases/resonant-publishes-groundbreaking-alzheimers-disease-research-with-the-potential-to-revolutionize-neurodegenerative-diagnostics-301984263.html
5. Kivisäkk P, Carlyle BC, Sweeney T, Trombetta BA, LaCasse K, El-Mufti L, Tuncali I, Chibnik LB, Das S, Scherzer CR, Johnson KA, Dickerson BC, Gomez-Isla T, Blacker D, Oakley DH, Frosch MP, Hyman BT, Aghvanyan A, Bathala P, Campbell C, Sigal G, Stengelin M and Arnold SE (2023) Plasma biomarkers for diagnosis of Alzheimer’s disease and prediction of cognitive decline in individuals with mild cognitive impairment. Front. Neurol. 14:1069411. doi: 10.3389/fneur.2023.1069411
6. Gamble, L.D., Matthews, F.E., Jones, I.R. et al. Characteristics of people living with undiagnosed dementia: findings from the CFAS Wales study. BMC Geriatr 22, 409 (2022). https://doi.org/10.1186/s12877-022-03086-4
