- On August 24, 2026, the U.S. FDA cleared a new single-biomarker blood test to help doctors detect signs of Alzheimer’s disease.
- The test helps doctors determine both rule-in (positive result) and rule-out (negative result) assessment of amyloid pathology, a hallmark of Alzheimer’s disease.
- The blood test is specifically for older adults 55 and older with signs or symptoms of cognitive decline.
Called the Elecsys® Phospho-Tau (217P) Plasma (pTau217) blood test, the test was developed in collaboration by pharmaceutical companies Roche and Eli Lilly and Company.
Medical News Today spoke with four Alzheimer’s disease experts to find out more about the Elecsys pTau217 blood test — how it works, how it’s different from the tests already used today for diagnosing Alzheimer’s disease, how people will be able to take the test, and how they predict this new test will change the Alzheimer’s disease diagnostic landscape.
According to Peter Gliebus, MD, chief of neurology and director of cognitive and behavioral neurology at Marcus Neuroscience Institute, a part of Baptist Health South Florida, the Elecsys pTau217 blood test works by detecting phosphorylated tau 217 in blood, one of the earliest and most specific blood indicators of Alzheimer’s.
“It rises early in the disease and remains mostly normal in other neurodegenerative conditions,” Gliebus explained. “Although it is a tau marker, blood pTau217 closely correlates with brain amyloid.”
Laura Nisenbaum, PhD, interim chief science officer of the Alzheimer’s Drug Discovery Foundation (ADDF), said the Elecsys test measures pTau217 concentration in plasma and uses validated cutoffs to categorize results as positive, intermediate, or negative.
“One of its distinguishing features is that it applies the same cutoffs across both primary and specialty care settings, which matters enormously for consistent, scalable implementation,” Nisenbaum told MNT.
The Elecsys pTau217 blood test is not the first Alzheimer’s test to be approved by the FDA.
“The FDA cleared the Lumipulse G pTau217/β-amyloid 1-42 Plasma Ratio [test] in May 2025,” Dung Trinh, MD, an internist for MemorialCare Medical Group and chief medical officer of Healthy Brain Clinic in Irvine, CA, told MNT. “That test measures two biomarkers and calculates a ratio. Roche also received FDA clearance in 2025 for its Elecsys pTau181 test, which is primarily intended to help rule out Alzheimer’s-related amyloid pathology in primary care.”
Trinh explained that what distinguishes the new Elecsys pTau217 test is that it is a single-biomarker assay that Roche says supports both rule-in (positive result) and rule-out (negative result) assessment of amyloid pathology, using the same validated cutoffs in primary and specialty care.
“That simplicity could be operationally important because one assay can potentially be used throughout the patient journey rather than requiring different testing strategies in different settings,” he continued.
MNT also spoke with Megan Glenn, PsyD, clinical neuropsychologist at the Center for Memory and Healthy Aging at the Hackensack Meridian Neuroscience Institute at Jersey Shore University Medical Center in New Jersey, who said that while we have seen several other blood markers explored over the last few years, many of them capture general brain inflammation or are easily affected by other neurological conditions.
“What makes this specific tau marker stand out is its strong connection to the exact amyloid plaques that are characteristic of Alzheimer’s disease,” Glenn explained.
“When compared directly to other options, this marker has consistently proven to be the most accurate at identifying these biological changes. It gives us a much clearer picture of what is happening biologically than previous blood tests could offer. This level of reliability is exactly what we need to confidently use blood testing in a clinical setting.”
— Megan Glenn, PsyD
“Because it is designed to run on Roche’s existing labs, it should be accessible through many of the same laboratories that handle routine blood work,” she said. “In practice, a patient experiencing cognitive symptoms would discuss testing options with their physician, who would order it as part of a broader evaluation.”
“The result, categorized as positive, intermediate, or negative for amyloid pathology, would then be interpreted alongside other clinical information to guide next steps. It is not a test patients can order themselves, and a positive result should always prompt further conversation with a clinician about what it means and what comes next.”
— Laura Nisenbaum, PhD
Trinh added that the FDA-cleared intended population is important to note for this test.
“This is for individuals aged 55 and older who are presenting with signs, symptoms, or complaints of cognitive decline,” he said. “It is not currently cleared as a general screening test for healthy, asymptomatic adults.”
Glenn said that the FDA clearance of this new blood test is a massive step forward in making cognitive evaluations more accessible for everyone.
“By using standard laboratory equipment, it brings advanced testing capabilities to a much wider group of patients who might never have had access to specialized brain scans,” she explained. “The most important thing to remember is that this test supports a careful clinical evaluation and does not replace a comprehensive assessment by a qualified professional.”
“This marks a significant inflection point, not just small news: it is the first FDA-cleared blood test that can both confirm and exclude Alzheimer’s amyloid pathology from a single blood sample, available on lab instruments already in thousands of hospitals,” Gliebus said.
“Just over a year ago, there were no FDA-cleared blood tests for Alzheimer’s — now there are four,” Nisenbaum commented. “That is a remarkable shift in a very short period.”
“The broader implication is that blood-based diagnostics are no longer a future promise. They are becoming part of routine clinical practice, and that changes how we think about everything downstream, from trial design to drug development to how patients and families get answers. The diagnostic landscape five years from now will look very different from the one we had just a year ago.”
— Laura Nisenbaum, PhD
Before incorporating the Elecsys pTau217 blood test into routine care, Trinh said there are several things he would want to very clearly understand. For example, he would want to see the complete FDA labeling and real-world performance data, not only overall accuracy, but the positive and negative predictive values in the types of patients he actually sees.
“Predictive value can change substantially depending on the prevalence of disease in the population being tested,” he explained. “Second, I would want to know more about the intermediate result group. A test can perform very well overall, but from a clinician’s perspective, the critical operational question is: How many patients fall into the gray zone, and exactly what should we do with them?”
Trinh said he would also want clinicians and readers to understand exactly what the test cannot tell us.
“Roche specifically states that it is not a stand-alone diagnostic test, and its safety and effectiveness have not been established for predicting who will later develop dementia or for monitoring treatment response,” he explained.
“A biomarker can tell us something very important about Alzheimer’s-related pathology, but caring for the patient still requires determining whether that pathology explains the symptoms, what stage of disease the person is in, what other conditions may be contributing, and what treatment or care plan is appropriate.”
— Dung Trinh, MD
