Detect Alzheimer’s years before symptoms show up: All you need are a blood test and brain scan

Yaffe has led research on modifiable dementia risk factors such as physical inactivity, cognitive inactivity, depression, smoking and cardiovascular health. According to her research, addressing these factors could delay or prevent up to 40 per cent of dementia cases. Alzheimer’s Disease, which is a form of dementia, is characterised by an abnormal and progressive buildup of two proteins in the brain — amyloid and tau. This accumulation forms destructive plaques and tangles that damage neurons, block cell-to-cell signals, and ultimately kill brain cells.

In recent years, blood-based biomarker tests measuring these proteins have emerged as a less invasive diagnostic approach. However, most previous studies have focused on older White adults, leaving limited evidence on how these biomarkers relate to cognition in midlife or in more diverse populations. The new study measured blood levels of Aß42, Aß40 and p-tau217 in 1,350 dementia-free adults in the US States, with an average age of 61 years. Researchers identified Alzheimer’s-associated biomarker levels in 86 participants — around 6 per cent of the study group.

At baseline, participants with elevated biomarkers demonstrated slower processing speed — the ability to quickly respond to changing information, such as traffic signals or conversations — as well as poorer executive functioning, which includes planning, organising and managing tasks like finances or schedules. Five years later, this group showed a 2.5- to 4-fold higher risk of rapid decline in verbal memory and a 3- to 4-fold higher risk of decline in processing speed, suggesting a significantly increased likelihood of developing Alzheimer’s disease.

Why experts urge caution

According to a 2025 report in the Indian Journal of Public Health, an estimated 5.3 million Indians are currently living with dementia, a number projected to nearly triple by 2050. Alzheimer’s disease accounts for 60 to 70 per cent of these cases. Dr Anil Venkitachalam, a Mumbai-based consultant neurologist not associated with the study, said that blood biomarkers currently have greater clinical relevance in patients who already show cognitive symptoms. “They may help differentiate Alzheimer’s Disease from other forms of dementia and assist in assessing prognosis and the expected rate of cognitive decline. They are also useful in identifying suitable candidates for clinical trials,” he said.

However, he cautioned against routine population-wide screening.“One important concern is the high potential for false positives,” Dr Venkitachalam said. “Many older individuals who are cognitively healthy may still show amyloid accumulation in the brain and yet never develop dementia.” In such cases, widespread screening could lead to unnecessary anxiety and psychological distress, especially since effective treatments for dementia remain limited. “Even if asymptomatic individuals are identified through biomarker testing, there is often no clearly established therapeutic pathway. Most professional associations therefore do not currently recommend routine biomarker testing in the general population,” he said. He advised individuals experiencing cognitive changes to consult neurologists or memory specialists for structured clinical evaluation before pursuing biomarker testing.

Blood tests as complementary testing

Unlike PET scans or spinal fluid tests used to detect tau and amyloid proteins, blood tests are relatively inexpensive and non-invasive. They are currently approved by the US Food and Drug Administration (FDA) for symptomatic patients but could eventually be expanded to include asymptomatic individuals.

New brain scan detects tau clusters earlier

In a separate development, researchers at the University of Pittsburgh School of Medicine have developed a new brain imaging test that may detect tau protein accumulation earlier than current clinical methods used in the US and Europe.

The study, also published in The Lancet, compared two PET scan tracers — compounds that bind to proteins and illuminate them during brain imaging — to assess their ability to detect tau tangles associated with Alzheimer’s Disease. Researchers found that the choice of tau tracer significantly influenced who tested positive for Alzheimer’s and who could qualify for treatment or clinical trials.“Tau is the biology most closely tied to symptoms and future decline,” said corresponding author Tharick Pascoal. “If we can detect tau earlier and stage it more precisely, we can make better decisions about who is truly on an Alzheimer’s trajectory. That matters for clinical trials now and could shape future clinical decision-making as new therapies emerge.”