Blood test may flag Alzheimer’s risk up to decade

A multinational study of 2,684 older adults found that a blood test measuring phosphorylated tau 217 (p-tau217) may flag people who could develop cognitive decline up to 10 years before symptoms appear. Participants with very high blood levels of the protein had an estimated 38% chance of impairment within five years and an estimated 78% chance within ten. The ten-year figure rests on much less data, so it is less certain. The results combine six observational studies and clinical trials in North America, Japan and Australia.

Predictive power beyond other markers

What makes p-tau217 useful is that it predicts decline even after researchers accounted for other known risk factors, including amyloid-beta plaques seen on PET scans and the APOE4 gene. Dr Rachel Buckley said the biomarker estimates an individual's level of risk, which goes beyond what genetics or brain imaging alone can show.

Despite the promise, the authors caution that blood tests are not yet recommended for routine screening of people without symptoms, because treatments that can change the course of the disease for those at high risk have not yet been established. Reisa Sperling said that until such therapies are proven, medical advice will stay the same whatever the test shows: exercise, a healthy diet and good sleep.

If future trials show that early treatment can slow the disease, the test could become a tool similar to cholesterol measurements in heart disease, helping doctors decide who should receive preventive therapy. For now, it mainly helps researchers identify people who may be suitable for prevention studies.