A simple blood test can detect Alzheimer’s disease early in people who visit their doctor with worsening memory.
Scientists in the US say the test could be used by practitioners within five years, and is more accurate and quicker than current methods.
The tool measures levels of a protein called tau in the blood, which is known to build-up in the brain and cause cell death.
Tau was found to be 3.5 times higher in the blood of people with Alzheimer’s disease than healthy people.
If used by doctors, the blood test could speed up diagnoses and fill gaps in clinical trials of new drugs.
At the same time, blood test results will help put minds at rest of people who wrongly fear they have Alzheimer’s – the most common form of dementia.
Currently there is no single test for dementia. A diagnosis is based on a combination of assessments such as pen and paper tests and brain scans.
A simple blood test can detect Alzheimer’s disease early in people who visit their doctor with worsening memory, researchers in California say
Senior author Professor Adam Boxer of the memory and ageing centre at California University in San Francisco, said the aim is for it to be used in GP surgeries for people with memory concerns.
He said: ‘It could identify people who should be referred to specialised centres to participate in clinical trials or to be treated with new Alzheimer’s therapies – once they are approved.’
The blood tests technique, described in Nature Medicine today, can swiftly reveal if a patient with memory issues has Alzheimer’s disease or mild cognitive impairment (MCI).
MCI causes memory problems that are either minor or severe, and can sometimes – but not always – lead to full blown dementia.
The test can also distinguish both conditions from frontotemporal dementia, a less common condition that begins around the age of 45 to 65 and is often misdiagnosed as Alzheimer’s.
The front and sides of the brain (the frontal and temporal lobes) are responsible for decision-making, behavioural control, emotion and language.
Alzheimer’s, on the other hand, damages the hippocampus and the back of the brain, deep inside memory circuits.
The test measures a protein called tau that accumulates in the brains of Alzheimer’s patients. Tau destroys brain neurons and leads to memory loss and confusion.
In a study led by UC San Francisco, researchers measured blood levels of phosphorylated tau 181 (pTau181).
A total of 362 people aged between 58 to 70 underwent testing, including 56 who had been diagnosed with Alzheimer’s, 47 with MCI, 190 people with different types of frontotemporal dementia and 69 healthy peers.
Levels of pTau181 were 3.5 times higher in those with the Alzheimer’s disease compared to healthy peers
But in patients with fronto-temporal dementia, amounts were within the same range as the control group.
Blood measures of tau were 8.4 pg/ml (picograms per millilitre) among people with Alzheimer’s, 3.7 among those with MCI and 2.4 among healthy people.
In people with fronto-temporal dementia, levels ranged from 1.9 to 2.8 pg/ml.
Professor Boxer said people with MCI would benefit from the test because they are at a higher risk of developing Alzheimer’s.
He said: ‘Being able to easily diagnose Alzheimer’s disease at early stages may be especially beneficial to patients with mild cognitive impairment, some of whom may have early Alzheimer’s disease.’
The key to beating the devastating illness lies in early detection so drugs can be administered at the most effective point.
It’s believed one of the reasons all potential medications have failed to date is they’re given at a late stage – when the condition is too far advanced.
What’s more, a jump in the number of Alzheimer’s patients enrolling in clinical trials will speed up the search for a cure.
In the US around 132 drugs for treating Alzheimer’s are being tested – 28 of which are in final large-scale trials before approval is sought from the Food and Drug Administration.
They include aducanumab – which it’s hoped may be the first drug that slows progression.
Professor Boxer said: ‘Individuals with early Alzheimer’s are more likely to respond to many of the new treatments that are being developed.’
Dr Sara Imarisio, head of research at Alzheimer’s Research UK, said: ‘A blood test for Alzheimer’s would be a simple, cost-effective and relatively non-invasive way to give key insights about disease processes underway in the brain.
‘We know the diseases that cause dementia begin decades before symptoms show, so a reliable blood test may one day be used to predict those with no obvious signs of disease who are most likely to go on develop dementia.
‘This test is still someway away from the point where doctors could use it to diagnose people in the clinic.’
Existing methods for diagnosing Alzheimer’s include measurement of the deposits of amyloid – another rogue protein implicated in dementia.
This is done using an expensive PET (positron emission tomography scan) or a painful and difficult lumbar puncture to count amyloid and tau in cerebro-spinal fluid.
The study follows research by other investigators published last year that found high levels of plasma amyloid were a predictor of Alzheimer’s.
But amyloid accumulates in the brain many years before symptoms emerge, said Professor Boxer.
He said: ‘In contrast, the amount of tau that accumulates in the brain is very strongly linked to the onset, the severity and characteristic symptoms of the disease.’
A companion study by Dr Oskar Hansson, of Lund University, Sweden, published in the same journal corroborated the results.
It found tau was a stronger predictor of developing Alzheimer’s in healthy older people than amyloid.
The researchers said they hope to see the blood test available in doctor’s offices within five years.
Alzheimer’s and other forms of dementia affects around 850,000 people in the UK – a figure set to rise to two million by 2050.