Blood test may help predict risk of cognitive decline due to Alzheimer's a decade before symptoms appear

A blood test that detects a protein linked to Alzheimer’s disease may help predict future cognitive impairment in older adults who are currently symptom-free, according to new research presented July 15 at the Alzheimer’s Association International Conference 2026 in London.

Dr. Ron Brookmeyer, distinguished professor in the UCLA Fielding School of Public Health’s Department of Biostatistics, is a co-author of the study – “Prognostic Value of Blood-Based P-Tau217 Levels for Progression to Cognitive Impairment" – which was published simultaneously in the Journal of the American Medical Association.

“What this research shows is we now have the tools to find who is at the highest risk of cognitive decline and dementia years before the onset of any symptoms and we can do it with a simple blood test,” said Brookmeyer, who served as interim dean and dean at UCLA Fielding from 2018-26 and has been a leading Alzheimer’s researcher since the 1990s. ”Identifying who is at high risk is important because treatments currently under development may work better in slowing or preventing dementia if started early before the onset of symptoms.” 

Specifically, researchers found that higher levels of the blood biomarker p-tau217 predicted faster cognitive decline. Cognitively healthy older adults with very high p-tau217 had an approximately 78% risk of developing cognitive impairment (defined as mild cognitive impairment or MCI, dementia or a consecutive clinical dementia rating or CDR, of 0.5) over 10 years, and about a 38% chance within five years. Researchers added that knowing factors other than p-tau217, like age, can improve individual risk predictions. The study was one of the largest and most comprehensive analyses to date examining the value of a p-tau217 blood test to predict the onset of cognitive decline and dementia.