Blood Testing & Genetic Testing for Alzheimer’s and / or Dementia

Last Updated: January 14, 2021


When a simple blood draw is all a doctor needs to diagnose Alzheimer’s disease or dementia, care will be revolutionized. Experts are working on blood tests that would eliminate the time, uncertainty and pain that are an unfortunate fact of diagnosing Alzheimer’s today.

Because early diagnosis makes a major difference in how well symptoms are managed, the impact would be huge. At least three different blood tests, and even a retinal test, are in development.

There is even a blood test for Alzheimer’s disease available right now.

On this page, we’ll describe what types of tests you can get this year, what will be available in the future, alternative testing options, and why the process for creating these tests takes so long.


Blood Tests Available Now

A blood test is available now, through your doctor, that delivers a result in about 10 days and accurately determines whether someone has Alzheimer’s disease. The Preclivity AD Test from C2N Diagnostics measures proteins in blood plasma that indicate a buildup of plaques known to cause dementia in people’s brains.


The cost of this Alzheimer’s blood test is $1,250, less expensive than a PET scan that looks for the same protein buildups. Unfortunately, the price tag cannot be covered by Medicare or Medicaid, but C2N says people who can’t afford the test can qualify for a discount based on their income.

Does it Work?

C2N Diagnostics says they tested Preclivity AD in 686 people and compared it to the results of PET scans. When PET scans showed a high amount of amyloid-beta, a protein that turns to plaques and tangles in the brains of people with Alzheimer’s, the blood test agreed 92 percent of the time. When the PET scan showed no amyloid, the blood test showed the same about 77 percent of the time.

How to Get the Blood Test

The Preclivity AD Test has not been approved by the Food and Drug Administration. It is currently available only through a doctor, and can be sold by the company under rules for commercial laboratories. The test, in other words, is available despite lacking FDA approval, though C2N has said the FDA is planning on reviewing the test in 2021. The Alzheimer’s Association says it won’t endorse the test until there is FDA approval.


Alzheimer’s Blood Tests Available in the Future

Another test that’s shown promise is called the Simoa (or SiMoA, for “single molecule array”) that also tests for proteins in blood plasma. It’s the same idea as other blood tests: identify “biomarkers” in the blood that can usually only be seen via expensive or difficult exams including PET brain scans, MRIs, and spinal taps. The specific protein Simoa can detect is called ptau181, and has been linked to the changes caused by dementia in the brain.

In studies, the Simoa was found to be as good at predicting the development of dementia as PET scans and a spinal tap, without the cost, pain, or radioactivity associated with those tests. And the test can also detect upcoming dementia-caused brain changes in both the short (within 15 months) and longer (four years) terms.  Right now, this technology is used by researchers to identify people who are good candidates for clinical trials. It is not yet available for most patients.


Alzheimer’s Genetic Tests

Genetic testing for Alzheimer’s or other related dementia is somewhat misleading. While blood tests will offer (hopefully) a definitive diagnosis, genetic testing only reveals a propensity for developing Alzheimer’s. Genetic tests reveal the presence of a gene or genetic mutation that has been linked to Alzheimer’s. By no means does having the gene or mutation guarantee that the individual will develop Alzheimer’s.

There are multiple types of dementia, well beyond Alzheimer’s, and the genetic markings for these other types of dementia are different. Some types of dementia, such as dementia resulting from Huntington’s disease, are more likely to have a hereditary component. Genetic testing for dementia is therefore not definitive, and the propensity to develop dementia varies with the type of dementia one might develop.

 Genetic testing for dementia differs from blood testing in significant ways. Genetic testing is available today, no prescription is required, and these tests are relatively inexpensive. They can be taken at home simply with a saliva swab. The cost is between $100 and $200.


Alzheimer’s / Dementia Testing Alternatives

Despite the lack of an FDA-approved blood test, families who suspect their loved one may have Alzheimer’s have a well-trod, if meandering, path to a diagnosis. To begin the process, there are online tests for Alzheimer’s that can be downloaded, printed, completed and taken to your doctor, and even some interactive tests that might provide immediate results. However, these online tests do not actually test for Alzheimer’s or dementia. Instead, they offer families answers to these questions: “Are my concerns about my loved one justified?” “Is this just normal aging or is there something more going on?” Officially, the tests are looking for Mild Cognitive Impairment (MCI). These tests are not definitive, but they can help a family figure out what their next step should be.

If a doctor suspects a patient may have Alzheimer’s, there are more definitive approaches. Brain scans and tests on extracted spinal fluid (a costly and painful procedure commonly referred to as a spinal tap) when coupled with multiple physicians’ consultations can make a diagnosis of Alzheimer’s with upwards of 90 percent accuracy. Families should expect their loved one to be evaluated by a neurologist, a psychiatrist, and very likely a psychologist as well. Since Alzheimer’s is so common among the elderly, a diagnosis is less about finding a condition which fits and more about eliminating other possibilities.


Future of Alzheimer’s Blood Tests

When blood tests become mainstream, they will significantly impact the way doctors diagnose and even treat the condition.

Beyond the Preclivity AD and Simoa described above, there are multiple other types of blood tests in development; some are looking at protective fats (called fatty amides) in the blood. Research shows that an increase in fatty amide levels indicates more beta amyloid in the brain. Beta amyloid plaques have been found in the brains of people with Alzheimer’s. (Healthy brains eliminate beta-amyloids before they turn to plaque.)

Other blood tests will measure proteins such as tau proteins and the neurofilament light chain (NfL) protein. Researchers have found that neuron (brain cell) death, characteristic in people with Alzheimer’s, may be detected by the corresponding increase of these proteins in the blood.

It is also possible that the probable link between insulin resistance, diabetes and Alzheimer’s means blood tests could show the disease in someone well before symptoms occur. Another protein called IRS-1 is commonly associated with diabetes but has also been linked to Alzheimer’s. Studies have shown that someone with Alzheimer’s has more IRS-1 than even someone with diabetes.

 Proteins associated with Alzheimer’s disease, including tau proteins that cause plaque buildup in the brain, are detectable through invasive spinal taps. A blood test would eliminate the need for a spinal tap, and could be administered in a doctor’s office rather than in the hospital.

Some of these are targeting the detection of Alzheimer’s three years in advance of symptoms, while others may detect the condition as far as 10 years in advance of physical symptoms. Regardless of the approach, blood tests significantly speed up the diagnosis process. Lab work will be able to detect Alzheimer’s in as little as 24 hours, compared with the many months it currently takes to receive a diagnosis. Patients, instead of being subject to a PET scan or a painful spinal tab, will simply give a blood sample. Because a blood test is a highly automated process, diagnosing Alzheimer’s becomes inexpensive and easy rather than time-consuming and involving multiple specialists. High accuracy allows for definitive answers, not families seeking opinions from multiple specialists.

Lastly, because blood tests will allow us to receive a diagnosis of Alzheimer’s long before we start to show any symptoms of the condition, it will change treatment. Rather than symptom management (the current strategy for combating Alzheimer’s), the focus becomes preventing or delaying the disease from progressing to where symptoms impact the life of the patient. It may be possible, for instance, to lessen the buildup of plaques in the brain through medication.


Other Tests (Besides Blood)

Another interesting finding in the study of Alzheimer’s is related to the eye. Researchers have found that people with Alzheimer’s have a part of their retina that is thinner than in people without the disease. It may be possible that a basic eye exam could, in the future, tell whether someone has Alzheimer’s or another dementia. And some of the proteins associated with Alzheimer’s (described above) can also be detected in eye fluid in the front part of the eye.

Advances in artificial intelligence have researchers excited about the potential for AI to predict the likelihood of developing Alzheimer’s, using only a blood sample and the answers to some basic questions about health.

There have even been promising developments in determining whether someone will develop Alzheimer’s based on their voice and the way they write. Neuropsychologists are analyzing voice recordings from people with dementia, and finding that the subtle differences in speech, including word choices and complexity of sentences, may be indicative of the disease. And differences in pen strokes, such as pauses someone takes when asked to draw a clock for the clock test, are another possible indicator.


What’s Taking So Long?

Everyone is impatient for a blood test to become mainstream; patients and families as much as researchers and doctors. So, why will it take so long? Part of the reason is the testing process. When a blood test is first developed, it is tested against persons currently known to have Alzheimer’s. But the goal is to identify persons well in advance of when they show symptoms. If a test correctly identifies those who already have Alzheimer’s, then it is tested against persons who do not currently have the condition but may be genetically predisposed to developing it.

If the researchers are hoping to identify the condition three years in advance of showing symptoms, then they must wait three years to determine if the test is working. If it is not, they start all over again. If they hope to identify the disease 10 years before symptoms, then they must wait 10 years.