A simple blood test could help identify people at increased risk of Alzheimer's-related cognitive decline years before they experience any noticeable problems with memory or thinking. In a large international study, researchers found that older adults with very high levels of a particular blood biomarker faced a 38% chance of developing cognitive impairment within five years. Over 10 years, the estimated risk rose to 78%, although the longer-term findings were based on substantially less data.
The findings offer new insight into the potential of blood tests to predict future cognitive problems in people who currently show no signs of impairment. The research was led by scientists at the Mass General Brigham Neuroscience Institute and involved teams working across three continents. The results were presented at the Alzheimer's Association International Conference and simultaneously published in JAMA.
The study focused on phosphorylated tau 217 (p-tau217), a blood biomarker associated with Alzheimer's disease. A test measuring this marker recently received federal clearance, raising hopes that blood testing could make Alzheimer's detection more accessible. However, an important question has remained: Can these tests reliably predict whether someone with normal cognitive function will eventually develop symptoms?
Blood Test Reveals Cognitive Decline Risk Years in Advance To investigate, researchers combined information from six observational studies and clinical trials conducted in North America, Japan, and Australia. Together, these studies included 2,684 older adults who showed no signs of cognitive impairment when they entered the research. At enrollment, participants provided blood samples that were analyzed for p-tau217.
They also underwent positron emission tomography (PET) brain scans, allowing researchers to establish baseline measurements of brain health. Annual follow-up assessments were then used to monitor changes in memory, thinking, and other cognitive abilities. The combined data covered an unusually long period.
Some participants entered one of the studies as early as 2004, while the most recent follow-up assessments took place in 2025. Across the studies, approximately 478 participants eventually developed cognitive impairment. When researchers compared these outcomes with the original blood test results, they found a strong relationship between higher p-tau217 levels and the likelihood of future cognitive problems.
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