Researchers found that a blood test measuring the biomarker p-tau217 helped estimate the likelihood of developing cognitive impairment over the next five to 10 years.
The study followed nearly 2,700 cognitively healthy older adults from six long-term research cohorts across Australia, North America and Japan.
Experts say the findings could eventually help identify people for prevention trials and guide future monitoring, though the test is not yet intended to predict an individual's future on its own.
For years, diagnosing Alzheimer's disease has often relied on brain scans, spinal fluid tests, or evaluating symptoms after memory problems begin. Now, researchers say a simple blood test could offer another important piece of the puzzle — helping estimate a person's risk of developing cognitive impairment years before symptoms appear.
The study focused on a blood biomarker called p-tau217, a form of the tau protein that's associated with Alzheimer's disease. Researchers found that higher levels of this protein in the blood were linked to a greater chance of developing cognitive impairment over the following five to 10 years, even among adults who had no noticeable memory or thinking problems when they entered the study.
The findings were presented at the Alzheimer's Association International Conference (AAIC) 2026 and published simultaneously in JAMA.
“Our findings provide some of the clearest evidence yet that elevated p-tau217 levels may help detect dementia risk years earlier — even in adults with no noticeable memory or thinking problems,” researcher Rachel F. Buckley, Ph.D., said in a news release.
“Once verified, these blood tests could be used to recruit patients for clinical trials of treatments to prevent cognitive decline and dementia. In the future, when treatments are approved for use early in the disease process, these tests could help guide monitoring, treatment decisions, and counseling for patients and families.”
How researchers studied the blood test
The study pooled data from 2,684 cognitively healthy older adults participating in six long-running research studies in Australia, North America, and Japan. Participants had blood samples collected at the start of the study, allowing researchers to measure p-tau217 levels before any cognitive symptoms developed.
Participants were then followed for as long as 13.5 years, with regular assessments of memory, thinking abilities, and daily functioning. Researchers used those real-world outcomes to estimate each participant's likelihood of progressing to cognitive impairment over two-, five-, and 10-year timeframes.
The researchers also compared the predictive value of the blood test with other established Alzheimer's risk measures, including brain imaging and genetic testing. Statistical models accounted for multiple factors to better understand how p-tau217 levels related to future cognitive decline across the study population.
What the findings could mean for consumers
Researchers found that participants with very high p-tau217 levels — more than twice the average level seen in the study — had an estimated 38% chance of developing cognitive impairment within five years and a 78% chance within 10 years.
Even people with moderately elevated levels faced a higher estimated risk, with approximately 15% risk over five years and 45% over 10 years. The blood test also provided predictive information beyond what brain scans and genetic testing alone could offer.
Still, researchers caution that the test is not a crystal ball. A person's p-tau217 level is only one factor influencing Alzheimer's risk. Age, genetics, kidney function, obesity, and racial and ethnic background can all affect biomarker levels and the likelihood of developing dementia.
For consumers, the findings are promising but not yet practice-changing. Researchers say the blood test could eventually help identify healthy older adults who are good candidates for Alzheimer's prevention trials or, in the future, guide earlier treatment and counseling if additional therapies become available. More research is still needed before the test can be used as a standalone tool to predict an individual's future risk.
“It is especially encouraging that the findings were so consistent across different groups and analyses, suggesting that we can now provide meaningful information to people about their future risk of developing impairment due to Alzheimer’s,” researcher Reisa Sperling, M.D., said in the release. “This information may become more relevant if current trials provide clear evidence that we can prevent cognitive decline with treatment if started before symptoms.”