A single blood test can now identify apparently healthy older adults who are likely to develop Alzheimer’s symptoms within five to ten years, according to findings presented at the Alzheimer’s Association International Conference in London and published in JAMA. Researchers from the Mass General Brigham Neuroscience Institute analysed data from 2,684 cognitively normal participants enrolled in long-running studies. Those with the highest levels of the blood marker p-tau217 faced a 38% probability of progressing to cognitive impairment within five years, rising to 78% within a decade. Participants with very low levels had a correspondingly low risk over the same period.

The test measures a phosphorylated form of tau that correlates closely with the accumulation of amyloid plaques and tau tangles, the defining neuropathology of Alzheimer’s. The data suggest the biomarker captures a tipping point in the disease process, where brain changes become significantly more likely to produce clinical symptoms. A separate study, not yet peer-reviewed, demonstrated that when primary-care physicians had access to p-tau217 results, their diagnostic accuracy for patients with cognitive complaints jumped from 62% to 88%. The test itself showed roughly 90% accuracy against PET scans or lumbar punctures.

These developments arrive as the therapeutic landscape shifts. Italian neurologists, addressing a Vatican-hosted conference on Alzheimer’s, stressed that early diagnosis is now essential because new immunotherapies targeting beta-amyloid can slow disease progression, provided they are administered in the initial stages. The same specialists noted that up to half of dementia cases may be preventable by addressing cardiovascular risk factors, social isolation, depression, and uncorrected vision or hearing loss. In Scotland, the BriDGe study is already offering p-tau181 and p-tau217 blood tests through more than 50 GP surgeries, aiming to refer up to 500 patients and accelerate diagnosis outside specialist centres. A Brazilian laboratory study, meanwhile, reported a graphene-based sensor that detected dopamine in artificial tears with near-perfect accuracy, though the work remains in vitro and has not been tested on human samples.

Caution persists. The blood tests are approved in the United States to aid diagnosis in symptomatic individuals, but researchers, including the JAMA study’s senior author, caution healthy people against seeking them out until interventions are proven for that population. An accompanying editorial noted the tests are not yet precise enough to guide individual prognosis, partly because the decade-long risk estimate rests on a smaller subset of participants. The next factual milestones will be results from the Scottish primary-care rollout and regulatory guidance on whether—and how—predictive blood testing should be deployed in asymptomatic adults.