A simple blood test could predict not only a person’s risk of developing Alzheimer’s disease, but also the year symptoms will begin.

Researchers at the Washington University School of Medicine in St. Louis set out to determine if levels of a specific protein in the blood could be used as a “biological clock” to predict when signs of the disease will emerge.

The specific protein, known as p-tau217, forms “tangles” in the brain that disrupt communication between nerve cells. In a healthy brain, tau helps to stabilize the structure of nerve cells.

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In some cases, brain scans can be used to detect these tangles when diagnosing Alzheimer’s. Preliminary studies have suggested that the same method could be used to determine a progression timeline.

As these imaging tests are often complex and expensive, the research team wanted to explore whether a blood test could monitor the same proteins and produce similar results.

The study, published in the journal Nature Medicine, analyzed data from more than 600 older adults enrolled in two long-term Alzheimer’s research projects.

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By comparing blood samples with participants’ cognitive performance over several years, the team found that p-tau217 levels rise in a “remarkably consistent” pattern long before memory loss begins, according to a press release.

The team then created a model that uses a patient’s age and protein levels to estimate when symptoms will appear, with a margin of error of three to four years.

“We show that a single blood test measuring p-tau217 can provide a rough estimate of when an individual is likely to develop symptoms of Alzheimer’s disease,” lead author Kellen K. Petersen, PhD, instructor of neurology at Washington University in St. Louis, told Fox News Digital.

The researchers found that older adults developed symptoms much more rapidly after p-tau217 became abnormal, he noted.

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“For example, people who first had abnormal p-tau217 levels around age 60 didn’t develop Alzheimer’s symptoms for about 20 years, whereas those who first had abnormal p-tau217 levels around age 80 developed symptoms after only about 10 years,” Petersen said. 

This suggests that age and disease-related changes in the brain can influence how quickly Alzheimer’s symptoms become apparent, the researcher concluded.

“At this point, we do not recommend that any cognitively unimpaired individuals have any Alzheimer’s disease biomarker test.”

“This could transform how researchers design clinical trials and, eventually, how clinicians identify people at highest risk for cognitive decline associated with Alzheimer’s years before decline begins,” Chicago-based Rebecca M. Edelmayer, PhD, vice president of scientific engagement at the Alzheimer’s Association, told Fox News Digital.

“A blood test is generally much less expensive and easier to administer than a brain scan or spinal‑fluid test. In the future, it could help doctors and researchers identify people who may benefit from early treatments,” added Edelmayer, who was not involved in the study.

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The study did have some limitations and caveats.

“We were only able to make predictions for individuals whose p-tau217 levels fell within a certain range, although it was a fairly wide range,” Petersen shared. “The models were developed in relatively healthy and well-educated research cohorts that were not diverse, so the results may not apply well to the broader population.”

While the researchers referenced in-home blood tests in this study, they cautioned against people seeking out and taking these tests themselves.

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“At this point, we do not recommend that any cognitively unimpaired individuals have any Alzheimer’s disease biomarker test,” Dr. Suzanne Schindler, a neurologist at Washington University who was a co-author of the study, said in the press release.

Peterson acknowledged that these results are still experimental and ripe for improvement.

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“The current estimate is not yet accurate enough for clinical use or personal medical decision-making, but we expect that it will be possible to create more accurate models,” he told Fox News Digital.

Looking ahead, the team hopes to refine the test by researching other Alzheimer’s-linked proteins to narrow the margin of error, Schindler said. More diverse participants are also needed to confirm the results.

Two large clinical trials are now in progress, aiming to determine whether people with high levels of this protein can benefit from treatment with one of two Alzheimer’s drugs before symptoms appear.

Lecanemab and donanemab are the only approved drugs designed to reduce levels of plaques in the brain associated with Alzheimer’s disease. Researchers hope that treating people earlier may boost the drugs’ effectiveness.

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“There are many other blood and imaging biomarkers, as well as cognitive tests, that we can combine with plasma p-tau217 to improve the accuracy of predicting symptom onset,” Petersen said. “We hope this work will lead to even better models that will be useful to individuals.”