Researchers at the Mass General Brigham Neuroscience Institute, working with teams across three continents, pooled data from six observational studies and clinical trials covering 2,684 older adults with no signs of cognitive impairment.

Blood samples taken at enrollment were analyzed for phosphorylated tau 217 (p-tau217), a biomarker associated with Alzheimer's disease. Approximately 478 participants later developed cognitive impairment.

Among those with very high biomarker levels, the estimated probability of impairment reached 38% within five years and an estimated 78% within 10 years, though the researchers noted far fewer observations supported the 10-year figure.

The results were presented at the Alzheimer's Association International Conference and published in JAMA.

The surprise is that a routine blood draw predicted future decline better than established risk factors. ScienceDaily reports that p-tau217's predictive value held even after researchers accounted for amyloid-beta plaques seen on PET brain scans and for known genetic risks such as APOE4.

Lead author Rachel F. Buckley, PhD, said the work estimates an individual's level of risk rather than simply identifying biological changes, calling the harmonized six-cohort data set large, varied and consistent.

A test measuring the marker recently received federal clearance, making accessible detection a realistic near-term prospect.

A second study underscores how routine blood values may flag dementia risk.

Research presented at the 39th ECNP Congress and published in the Journal of Alzheimer's Disease analyzed 316,542 Korean adults over 15 years, finding the lowest hemoglobin group had a 16% higher dementia risk and the highest a 7% higher risk, Medical News Today reports.

Vascular dementia risk rose about 18-19% at both extremes, while Alzheimer's risk rose 14% only at low levels, with a stronger association in women. Experts stress hemoglobin does not cause dementia but may mark underlying conditions like iron deficiency or kidney disease.

Blood tests are not yet recommended for screening people without symptoms, because disease-modifying treatments for asymptomatic high-risk individuals have not been established.

"Our medical advice would remain the same regardless of test results: exercise regularly, maintain a healthy diet, and prioritize sleep and overall wellness," senior author Reisa Sperling, MD, told ScienceDaily.

The long-term goal, she said, is to make p-tau217 testing as routine as cholesterol testing for heart attack risk. For now, the biomarker can identify high-risk candidates for prevention trials, and ongoing therapy studies could quickly change the preventive care landscape.