Blood test can detect dementia in women 25 years before symptoms begin

A protein measured in blood samples is "strongly linked" to the future onset of the debilitating condition, say American scientists.

They believe their findings open the way to earlier prevention strategies and more targeted monitoring, instead of waiting until memory problems kick in.

The study shows that higher levels of the biomarker phosphorylated tau 217 or p-tau217 - a protein linked to the brain changes seen in Alzheimer’s disease - were associated with future mild cognitive impairment and dementia among older women.

First author Dr. Aladdin Shadyab from the University of California, San Diego, said: “Our study suggests we may be able to identify women at elevated risk for dementia decades before symptoms emerge.

“That kind of long lead time opens the door to earlier prevention strategies and more targeted monitoring, rather than waiting until memory problems are already affecting daily life.”

The findings, published in JAMA Network Open, are based on data from 2,766 female participants

who enrolled in a study, aged 65 to 79, in the late 1990s and were followed for up to 25 years.

All the women were dementia free at the start of the study.

Blood samples collected at the outset were analysed years later to measure p-tau217, a form of tau protein that reflects early brain changes associated with Alzheimer’s disease - the most common form of dementia.

Over the following years, researchers identified women who developed memory or thinking problems, including dementia.

Those who had higher levels of p-tau217 in their blood at the start of the study were "much more likely" to develop dementia later in life.

As levels of the biomarker increased, so did dementia risk.

Women with the highest p-tau217 levels faced the greatest likelihood of developing dementia over the long term, according to the findings.

But the researchers also found that the risk of cognitive impairment or dementia associated with higher levels of p-tau217 was not the same for everyone.

For example, higher p-tau217 levels were more strongly associated with poorer cognitive outcomes among women over the age of 70 than those younger than 70 at the outset and among those with the APOE ε4 genetic risk factor for Alzheimer’s disease.

The study also found that p-tau217 was more predictive of dementia among women who had been randomised to oestrogen plus progestin hormone therapy compared to a placebo.

The strength of the association also differed between white and black women, but combining p-tau217 with age improved dementia prediction similarly in both groups.

Study senior author Dr. Linda McEvoy said: “Blood-based biomarkers like p-tau217 are especially promising because they are far less invasive and potentially more accessible than brain imaging or spinal fluid tests.

“This is important for accelerating research into the factors that affect risk of dementia and for evaluating strategies that may reduce risk.”

Blood-based biomarkers are not currently recommended for clinical use in people who don't have symptoms of cognitive impairment.

The researchers say that additional studies are needed to determine how p-tau217 testing might be used in routine clinical care.

They said future research will also explore how factors such as hormone therapy, genetics and age-related health conditions interact with plasma p-tau217 throughout someone’s life to affect the risk of dementia.

Dr. Shadyab added: “Ultimately, the goal is not just prediction, but using that knowledge to delay or prevent dementia altogether.”