Alzheimer's Blood Tests: How Do They Work and Should You Request One?

Worldwide, at least 50 million people are believed to be living with Alzheimer’s disease or other dementias, and accuracy and timing of diagnosis are critical. In the United States, Alzheimer’s blood tests are now available as another tool that can provide highly accurate, direct evidence of amyloid buildup in the brain earlier and faster than before. This makes it possible for people with Alzheimer’s to proceed to next steps, such as learning about the  disease, finding the right care team, making healthy lifestyle changes to protect their brain, and starting beneficial treatments.

Detecting and diagnosing Alzheimer’s disease

Diagnosing Alzheimer’s usually involves neuropsychological assessments as part of the evaluation. These cognitive examination aids, along with other screening methods such as cerebrospinal fluid (CSF) analysis or brain imaging using positron emission tomography (PET) scans, can check for Alzheimer’s biomarkers and toxic protein buildup in the brain. In a primary care setting, however, it is often difficult for providers who do not have expertise in neurological disorders to discuss diagnostic or treatment options with their patients.

In recent years, Alzheimer’s blood tests have emerged as a tool to aid primary care physicians in their initial examinations of people who are showing symptoms of cognitive impairment. By looking at the presence of Alzheimer’s-related proteins in the blood, these tests serve as an important first step in determining the next steps for treatment.

It’s important to emphasize that a blood test alone cannot diagnose Alzheimer’s disease. These tests provide important early information that is used as part of a comprehensive clinical evaluation of cognitive impairment. Blood tests can help to rule out Alzheimer’s as a cause of an individual’s memory decline, prompting a person’s clinical team to look at other conditions that may be treatable or even reversible. More recently, blood tests are also able to “rule in” Alzheimer’s, a finding that could lead clinicians to investigate further with additional tests.

FDA-cleared Alzheimer’s blood tests

Alzheimer’s Disease Research, a BrightFocus Foundation program, provided pivotal early grant support for the first Alzheimer’s blood test to come to market: C2N’s PrecivityAD™ test, which became commercially available in the U.S. in late 2020. Since then, numerous other tests have been developed, with four now cleared by the U.S Food and Drug Administration (FDA), with the most recent two being cleared in August 2026:

• Lumipulse (Fujirebio)
• pTau181 (Roche)
• PrecivityAD2 (C2N)
• Elecsys® pTau217 (Roche)

How the FDA-cleared tests work

In general, Alzheimer’s blood tests measure the amount of specific proteins linked to Alzheimer’s (referred to as “biomarkers”) that are present in the blood. The specific biomarkers vary depending on the test, but all use their measurements to calculate the likelihood that someone has or does not have the amyloid plaques that are a hallmark of Alzheimer’s.

Elecsys pTau217 measures how much of a specific form of a protein, tau, is floating freely in the blood. The presence of this biomarker protein, pTau217, has been linked to Alzheimer’s-related changes in the brain. Elecsys pTau217 is the first FDA-cleared single biomarker Alzheimer’s blood test for people age 55 and older who have shown signs of cognitive decline.

pTau181, an earlier test developed by Roche, measures a different form of tau. Importantly, this test is only intended to rule out Alzheimer’s as a potential diagnosis. It is not intended to “rule-in” Alzheimer’s, which is one advantage of the newer Elecsys pTau217 test.

The PrecivityAD2 test, in addition to tau, looks at the ratio of two types of amyloid-beta (Aß) protein in the blood: Aß40, the most prevalent type in the brain, and Aß42, which is less prevalent in the brain but makes up the majority of Aß protein found in Aß plaques. The test also measures apolipoprotein E (ApoE) variants in the blood to determine whether a person carries the APOE4 mutation, which raises the risk for brain Aß accumulation and Alzheimer’s disease. This test is noteworthy in that it is available to people as young as 40 years old who have cognitive impairment.

The Lumipulse test from Fujirebio Diagnostics measures the same two forms of amyloid-beta as PrecivityAD2—Aß42 and Aß40–and is intended for adults 55 and older who are being evaluated for signs of cognitive impairment.

Accuracy of tests varies according to populations studied

Despite recent progress, there are a few hurdles to overcome before Alzheimer’s blood tests are ready for widespread use. Data on their accuracy comes almost exclusively from clinical trials, where participants tend to be alike in age, race, and ethnicity, as well as Alzheimer’s risk factors. In community settings, people taking the test would vary in all these aspects.

Clinical data supporting the FDA clearance of PrecivityAD2 showed that it provided consistent results regardless of the participant’s ethnicity, sex, age, or APOE4 status. In addition, the test performed consistently in people with common conditions like diabetes, chronic kidney disease, and atrial fibrilation, which can sometimes interfere with the accuracy of blood-based tests.

A 2022 study evaluated the use of p-tau181 and p-tau217 blood biomarkers among patients enrolled in the Mayo Clinic Study of Aging. It showed that results were not as accurate as those previously reported in patients seen in specialized memory clinics, and that multiple comorbidities, including chronic kidney disease or a history of myocardial infarction or clinical stroke, were associated with higher plasma p-tau levels, which in some cases produced a false positive result.

Should you request an Alzheimer’s blood test?

If you are not showing signs of cognitive decline, the answer is simple: no, you should not request an Alzheimer’s blood test. As of now, these tests are intended solely to check whether a person’s symptoms are possibly the result of Alzheimer’s-related changes in the brain or due to other conditions. If you or someone close to you thinks that you might be showing symptoms related to cognitive decline, you should discuss testing options with your primary care physician or a neurologist.

In a recent conversation with BrightFocus, Dr. Suzane Schindler emphasized this point:

“There are lots of people who are biomarker-positive, who already have these plaques and tangles, who will never develop symptoms during their lifetime. As a clinician, at this point in time, my recommendation for cognitively unimpaired individuals is not to do testing.”

One aspect related to the tests that remains murky is cost. Dr. Schindler was open about the fact that the science has outpaced the paperwork, saying, “…all of these tests are new in the last five years, and regulations and reimbursement really trail what’s new.” Whether private health insurance or Medicare will cover the cost of tests is not consistent. It is recommended that people check the test manufacturers’ websites directly for the most up to date information about cost and possible payment options.

The bottom line

Although Alzheimer’s blood tests are becoming more available in the U.S., physicians and experts are recommending a measured approach to their use. People should only consider taking one of these tests if they are already being evaluated for cognitive impairment. At this time, it is not recommended that people take an Alzheimer’s blood test as a part of routine, preventative care.

If a doctor is not comfortable ordering the test, they might be able to refer the patient to a memory clinic or Alzheimer’s Disease Research Center  where the tests are used. Another option is joining a clinical trial or study where Alzheimer’s blood tests are used to screen participants.

BrightFocus-funded scientists are researching other novel ways to detect and reduce Alzheimer’s risk and innovative tools for diagnostics. Explore our funded research.