Blood Test Predicts Alzheimer's Symptom Onset Within Three to Four Years in Study

A new blood test that measures levels of p-tau217, a protein that builds up in the brain during Alzheimer's disease, shows promise for predicting symptom onset but raises questions about its accuracy and reliability.

A study funded by the National Institutes of Health tested the blood test in more than 600 older adults without symptoms. The repeated tests predicted the age of symptom onset with a median absolute error of three to four years. Higher p-tau217 levels linked to earlier symptoms.

Researchers found that people with elevated p-tau217 at age 60 typically developed symptoms about 20 years later. Elevation at age 80 led to symptoms after roughly 11 years.

The findings appear in Nature Medicine. The researchers said validation is needed in broader, more diverse groups. They noted the test's accuracy may not suffice for individual clinical decisions yet.

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

Sheena Aurora, MD, vice president of medical affairs for the Alzheimer's Association in Chicago, said demand grows for biomarkers to confirm the disease as treatments emerge. "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," she told Fox News Digital.

The tests cost less and prove easier to access than PET scans or MRIs, Aurora said. "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."

Two blood tests have FDA clearance: the Fujirebio Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio for symptomatic adults 55 and older, and the Roche Elecsys pTau181 Plasma for initial assessment in primary care for adults 55 and over with cognitive decline symptoms.

Several lab-developed tests exist, but they vary and have limits, Aurora noted. The Alzheimer’s Association guidelines recommend blood tests mainly in specialized settings for patients with cognitive impairment, where evidence supports their use.

"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."

Diagnosing Alzheimer's involves a multi-step process with various tests, and blood tests form one part, Aurora said. "Current Alzheimer’s blood biomarker tests are not a standalone test to diagnose Alzheimer’s disease – such a thing does not yet exist."

Blood tests require ordering and interpretation by healthcare professionals in a clinical context, she added. Guidelines warn that test accuracy varies, and many on the market do not meet performance standards.

False positives pose a risk of anxiety. People with chronic kidney disease, for instance, may show high biomarker levels without the disease.

Aurora called for better education for patients and providers, plus clear follow-up after results. "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."

The Alzheimer’s Screening and Prevention (ASAP) Act seeks to expand access by creating a Medicare pathway for FDA-approved or cleared blood biomarker screening tests. Medicare now covers preventive services only if Congress authorizes them or federal guidelines recommend them.