Alzheimer's blood test may predict symptoms years in advance

Alzheimer's blood test may help identify older adults who are likely to develop symptoms within the next five to 10 years, according to new research, although scientists say the test is not yet ready for routine use in healthy people.

The study, published in JAMA and presented at the Alzheimer's Association International Conference in London, found that symptom-free adults with the highest levels of the blood biomarker p-tau217 faced a significantly greater risk of developing cognitive impairment over the following decade.

CBS News reported researchers said the findings could help accelerate clinical trials by identifying people most likely to benefit from experimental Alzheimer's prevention treatments.

High p-tau217 levels linked to greater Alzheimer's risk

The research team from Mass General Brigham analysed data from 2,684 older adults who were cognitively healthy when they enrolled in long-running Alzheimer's studies.

Participants received a p-tau217 blood test when they joined the studies and underwent annual cognitive assessments. Between the earliest enrolment in 2004 and last year, 478 participants developed cognitive impairment.

Researchers found that adults with very high p-tau217 levels had a 38% chance of developing cognitive impairment within five years. That risk increased to 78% over 10 years.

By comparison, participants with very low p-tau217 levels had a much lower likelihood of developing cognitive problems during the same period.

Researchers say healthy adults should not seek the test yet

Dr Reisa Sperling, senior author of the study and director at the Mass General Brigham Neuroscience Institute, cautioned that healthy people should not rush to request the blood test because there are currently no proven preventive treatments based on the results.

"Wait and get tested when you can potentially do something about it," Sperling said.

"At this point, it wouldn't change what I would tell someone to do. I'd still tell them to eat well, sleep well, exercise a lot and stay engaged."

The p-tau217 test is currently used to help doctors determine whether people already experiencing memory or thinking problems have Alzheimer's disease rather than another neurological condition.

Blood marker offers clues to Alzheimer's progression

Scientists believe Alzheimer's disease is characterised by two major brain changes: the build-up of amyloid plaques and tau tangles, which damage brain cells.

The p-tau217 blood test measures a form of the tau protein that closely reflects the amount of amyloid plaque accumulation and may also indicate the development of harmful tau tangles.

"This is a gradual process where amyloid and tau build up in the brain and this blood-based biomarker is telling you how far you are in that process," Sperling said.

Researchers added that while moderate p-tau217 levels indicated gradually increasing risk, only the highest levels appeared to correspond with the biological tipping point associated with future symptoms.

Experts urge caution despite promising findings

Experts who were not involved in the study welcomed the findings but said more evidence is needed before the blood test can reliably predict Alzheimer's risk for individual patients.

In an accompanying JAMA commentary, Dr Suzanne Schindler of Washington University in St Louis and Dr David Wolk of the University of Pennsylvania noted that relatively few participants had been followed for the full 10 years, making the longer-term estimates less certain.

They also said factors such as cardiovascular disease or death from other causes could influence the results.

"The blood tests are not yet precise enough to guide individualized prognosis," they wrote, while describing the research as "a crucial piece of the puzzle."

Jessica Langbaum of the Banner Alzheimer's Institute added that although people with a family history of Alzheimer's are already asking for the test, she currently advises against it until studies determine whether early treatment can prevent symptoms from developing.