Those testing positive were found to be more likely to develop early markers of the disease within five years
A groundbreaking study has revealed a simple blood test measuring a biomarker known as p-tau217 could forecast dementia risk in older adults who show no cognitive symptoms.
The research found individuals with elevated levels of this protein in their bloodstream faced an estimated 38 per cent higher likelihood of developing early dementia indicators within five years.
Over a decade, this risk climbed to 78 per cent, although researchers noted the longer-term data was less robust.
"What this tells me is that we really can use p-tau217 blood tests in future to be able to understand somebody's individual risk of cognitive impairment," said lead study author Rachel Buckley, an associate professor of neurology at Harvard Medical School.
Conventional Alzheimer's diagnosis has long relied on costly and invasive methods like PET scans or lumbar punctures.
But blood tests detecting phosphorylated tau 217 offer a less burdensome alternative that can "strongly predict" the accumulation of beta-amyloid plaques in the brain, according to Ms Buckley.
These sticky plaques trigger inflammation and disrupt neuronal communication, potentially building up decades before any memory problems emerge.
As amyloid accumulates, tau proteins form tangles within brain cells, ultimately causing neurones to deteriorate and perish.
Ms Buckley, who also works at the Mass General Brigham Neuroscience Institute in Boston, explained the significance of combining these markers.
"However, if an early stage of tau is combined with very elevated levels of amyloid, amyloid appears to be the match that lights the fire for the spread of disease across the brain," she said.
Despite the promise of these blood tests, experts caution against relying on them exclusively for diagnosis.
Dr Richard Isaacson, director of research at the Institute for Neurodegenerative Diseases in Florida, who was not involved in the study, emphasised the need for comprehensive assessment.
Dr Isaacson said: "Never would I order a p-tau217 test in isolation. Why? For one, it tells you only one small part of what is most often a complicated biological picture."
He noted factors such as a common cold or kidney problems could distort results, increasing the chance of false positives.
Rather than using these tests solely for diagnosis, Isaacson employs them to monitor how patients respond to treatment and lifestyle modifications.
Research suggests up to 45 per cent of dementia cases might be prevented through interventions including exercise, improved diet, social engagement and management of metabolic risk factors.
The findings, presented at the Alzheimer's Association International Conference and published in JAMA, drew upon six observational and clinical trials conducted across Australia, North America and Japan.
Nearly 2,700 symptom-free older adults underwent both PET brain scans and p-tau217 testing at the outset, with follow-up periods extending to 21 years.
Crucially, the blood test results proved significant regardless of brain scan findings or genetic risk factors such as the APOE4 variant.
Buckley acknowledged the research remains preliminary and requires replication in broader, more diverse populations.
Currently, these tests are not recommended for cognitively healthy individuals.
"Hopefully, p-tau217 tests can one day function like tests that measure your risk of developing diabetes or having a heart attack, but this test would be for your risk for Alzheimer's disease and dementia," Ms Buckley said.
