Alzheimer's blood tests may predict symptoms years in advance, but experts urge caution

A new wave of blood tests aiming to predict Alzheimer’s risk may offer hope for earlier detection — but they could also raise concerns about the accuracy and reliability of the results.

A recent study funded by the National Institutes of Health evaluated a blood test measuring levels of p-tau217 (phosphorylated tau 217), a protein that accumulates in the brain during Alzheimer’s disease.

In a group of over 600 older adults without symptoms, repeated blood tests were found to predict the age of symptom onset with a median absolute error of about three to four years. Higher levels of p-tau217 were associated with earlier emergence of symptoms.

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Someone whose p-tau217 levels are elevated at age 60 would typically develop symptoms around 20 years later, the researchers found. If p-tau217 becomes elevated at age 80, symptoms tend to appear much sooner, after about 11 years.

The findings, published in Nature Medicine, need to be validated in broader and more diverse populations, the researchers noted. The test's predictive accuracy may not yet be sufficient for individual clinical use.

"In the near term, these models will accelerate our research and clinical trials," said lead investigator Dr. Suzanne Schindler at Washington University in St. Louis in an NIH press release. 

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"Eventually, the goal is to be able to estimate when individuals are likely to develop symptoms, which will help them and their doctors to develop a plan to prevent or slow symptoms."

As more Alzheimer’s treatments are becoming available, there is a growing demand for biomarker confirmation of the disease, according to Sheena Aurora, MD, vice president of medical affairs for the Alzheimer's Association in Chicago.

"Blood-based biomarker tests can improve the accuracy and speed of diagnosis when used as a complement to other testing, offering a path to earlier Alzheimer’s detection," Aurora told Fox News Digital.

The tests are relatively inexpensive and easier to access compared to PET scans or MRI, according to the expert.

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"For many, early detection can bring peace of mind, time to plan ahead, agency over decisions and the opportunity to try treatments that slow disease progression," she said.

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Two Alzheimer’s blood tests have been cleared by the FDA – the Fujirebio Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio, cleared for symptomatic adults 55 and older, and the Roche Elecsys pTau181 Plasma, cleared for initial assessment in primary care for adults 55 and over with symptoms of cognitive decline.

Several other lab-developed tests are also emerging – but not all tests are the same, and they do have limitations, Aurora noted.

The Alzheimer’s Association’s clinical guidelines recommend using blood tests primarily in specialized care settings for patients with cognitive impairment, as that is currently the only context where strong evidence supports their effective use, according to Aurora.

"We do not recommend the use of blood biomarker tests in people who are not experiencing symptoms," she said. "There currently is not substantive data about use of these tests in primary care settings or for people who are not cognitively impaired."

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Diagnosing Alzheimer’s is typically a "multi-step process" involving several types of tests, Aurora noted, but blood testing can be an important piece of the diagnostic process.

"Current Alzheimer’s blood biomarker tests are not a standalone test to diagnose Alzheimer’s disease – such a thing does not yet exist," she said.

Blood tests are not a substitute for a comprehensive clinical evaluation, the expert noted, "and they should be ordered and interpreted by a healthcare professional in the context of clinical care."

The Alzheimer’s Association’s guidelines also warn that accuracy can vary widely among tests, and that many blood biomarker options on the market fall short of recommended performance standards.

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There is also a risk of false positives, which can cause significant anxiety, experts warn. 

Research shows that people with chronic kidney disease, for example, may have higher levels of Alzheimer’s blood biomarkers, even when the disease is not present. This underscores the importance of healthcare providers carefully analyzing the test results.

As new research continues to show the promise of blood tests, Aurora stressed the need for better education for both patients and providers — along with clear clinical follow-up after results — to fully realize their potential across different care settings.

"Studies in these areas are being conducted, and we expect to learn more at the 2026 Alzheimer’s Association International Conference (AAIC 2026), July 12-15 in London and online," she added.

Aurora noted that the Alzheimer’s Screening and Prevention (ASAP) Act aims to expand access to new blood tests by creating a pathway for Medicare to cover FDA-approved or cleared blood biomarker screening tests. 

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Under current law, Medicare can only cover preventive services if Congress authorizes them or federal guidelines recommend them, a limitation that has delayed coverage of emerging Alzheimer’s tests.