Blood test could detect Alzheimer's signs 'decades before symptoms appear', study shows

A blood test could detect Alzheimer's decades before symptoms appear, a study suggests.

The findings show the disease may be present in midlife and already linked to cognitive differences, researchers said.

Using blood tests that measure the hallmark proteins associated with Alzheimer's to pinpoint changes in the brain earlier "could be incredibly valuable", according to experts.

When these proteins, called amyloid and tau, abnormally build up in the brain, Alzheimer's happens.

Researchers measured the levels of two amyloid biomarkers, as well as p-tau217, in the blood of 1,350 people without dementia in the US. The average age of patients was 61.

Analysis found high levels of the biomarkers in 86 patients, who also saw worse cognitive performance, accelerated decline of verbal memory, and slower processing speed in tests taken five years apart.

While more research is needed, the latest results build on previous studies with older patients by "showing that evidence of Alzheimer's disease neuropathology is present in midlife, although infrequent, and is already linked to measurable cognitive differences", researchers said.

"These findings support the concept that Alzheimer's disease begins decades before clinical symptoms emerge and highlight the potential value of plasma biomarkers for early detection in the general population," they said in the study published in The Lancet.

"Identifying individuals with early Alzheimer's disease neuropathology through accessible, blood-based assays could help target preventive strategies and clinical trials aimed at delaying or preventing the onset of dementia, with implications for both clinical practice and public health policy."

Brain scans could also detect tau protein tangles

In a separate study published in the journal, it is suggested that a new way of performing brain scans could detect tau protein tangles before symptoms appear.

Researchers compared Flortaucipir, a radioactive tracer used in PET scans, to a newer agent called MK6240, in 682 patients in the US and Canada, finding more than twice as many tau-positive cases as Flortaucipir in early tau regions.

Flortaucipir, which is also known as Tauvid, is licensed in the UK but not routinely used on the NHS.

About a million people in the UK have dementia and this figure is expected to rise to 1.4 million by 2040, according to estimates.

Alzheimer's - the most common form of dementia - makes up between 60% and 80% of cases.

Dr Jacqui Hanley, head of research funding at Alzheimer's Research UK, said the two studies "add to a growing body of evidence showing progress in detecting the biological changes linked to Alzheimer's disease much earlier in life, using a range of biomarkers from blood tests through to advanced brain imaging".

"Being able to identify these changes sooner than we can now could be incredibly valuable.

"If we can identify Alzheimer's disease earlier on, it would open up opportunities for people to take part in studies of new treatments. We could also identify people who might benefit from disease-modifying treatments that are indicated for early-stage disease.

"In the UK, many people wait far too long for a dementia diagnosis, meaning they often miss out on these opportunities."

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She said blood tests to potentially detect Alzheimer's are less invasive, scalable and potentially more accessible than existing tools such as PET brain scans and lumbar punctures.

"Detailed brain imaging remains important for understanding the extent and stage of disease more precisely, which is critical for research and treatment decisions," she added.

"The study of tau PET scans suggests newer methods might detect Alzheimer's-related changes earlier than existing techniques."

Blood tests for dementia diagnosis could be available on the NHS by 2029 under the Blood Biomarker Challenge, a multimillion-pound initiative led by the Alzheimer's Society, Alzheimer's Research UK, and the National Institure for Health and Care Research.

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