New Alzheimer's blood test offers hope but experts urge caution

A new Alzheimer's blood test that promises to detect the disease years before symptoms develop has won support, but some experts have urged caution over its wider use.

The blood test measures levels of a protein called p-tau217, which signals changes in the brain associated with the development of Alzheimer's disease that begins up to 15 years before symptoms start.

The effectiveness of the test was described in the Jama Neurology journal as “accurate” for diagnosing people with suspected Alzheimer's disease, which is responsible for between 60 per cent to 80 per cent of dementia cases.

“The blood test is sensitive enough to detect changes at the time – before the real big changes in thinking occur – when treatment might be able to halt or reverse the progression [of the disease],” said Prof Paul Matthews, associate director of the UK Dementia Research Institute.

Prof Matthews, who works at Imperial College London, said that the blood test could potentially be used to screen large numbers of people to determine who might need to be given the next generation of Alzheimer’s disease treatments.

“If we could do this for everyone at 50 or 65, we could detect who is really at high risk. In a perfect world, when we have a treatment that could be deployed, these people could be treated to prevent the disease,” he said.

Dr Ivan Koychev, a senior clinical researcher in the Department of Psychiatry at the University of Oxford, described the new study as the latest in a series that has shown that blood biomarkers “are becoming very promising in terms of being able to detect whether someone has Alzheimer’s disease pathology”.

This means that the person has biological characteristics associated with the disease, although they may not necessarily have symptoms.

“They have shown the blood biomarkers are as good at identifying people with Alzheimer’s disease pathology as more expensive and more invasive tests, like lumbar puncture,” he said.

A lumbar puncture, also known as a spinal tap, involves a needle being inserted into the lower back to remove fluid, which can then undergo laboratory testing.

Also, brain scans may be used to look for the build-up of amyloid plaques, which are protein aggregations associated with Alzheimer’s disease.

However, Prof Paul Morgan, of the UK Dementia Research Institute at Cardiff University in the UK, cautioned that while the new test may help to identify those at high risk of developing Alzheimer's disease, there were still limited treatment options available to treat them.

“It’s a step forward [but] it might not be, at the moment, transformative,” he said.

He added that identifying people at high risk of developing Alzheimer's disease could be useful for selecting people for clinical trials, which could aid the development of new treatments.

If clinical trials involve only people at high risk of developing Alzheimer’s disease, it increases the chance that they will be able to detect whether drugs are effective or not than if trial participants are drawn from the general population.

Prof Morgan said that the new blood test appeared to be more straightforward than other Alzheimer’s disease pathology blood tests, which may involve “several different measures and you mix them up to get a good prediction”.

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In recent years, a number of drugs have been approved for the treatment of Alzheimer's disease and, unlike previous-generation medication, are able to combat the underlying pathology, or biological changes associated with the disease, rather than managing the systems.

These amyloid-clearance therapies have been shown to have some effect in clearing amyloid plaques, which are protein aggregations linked to Alzheimer’s disease.

In clinical trials, one drug – Leqembi or Lecanemab – slowed the progression of symptoms in slightly more than a quarter of patients who were in the early stages of Alzheimer’s disease.

Hope for further treatments

Treatments have yet to be developed that could actually stop or reverse the disease’s progression, or that could prevent the onset of symptoms in people who have yet to develop the disease.

However, given the progress made with Alzheimer’s disease drugs in recent years, despite decades of false starts, some researchers are hopeful that such more advanced therapies could be developed in future.

Involving 786 participants, the recently published study found that the new blood test, which looks for the p-tau217 protein, was highly accurate at identifying elevated levels of beta amyloid and at identifying pathologies linked to the build-up of another protein associated with Alzheimer’s disease, tau.

Beta amyloid accumulates in patients’ brains for as long as two decades before Alzheimer’s disease symptoms become apparent, so detecting it early – and potentially starting preventive treatments, should they become available in future – may offer benefits.

Exploring a 'prickly issue'

Rob Howard, professor of old age psychiatry at University College London, described the use of blood tests such as the one analysed in the new study as “such a complicated and prickly issue”.

A key concern of his is that many people who have evidence of Alzheimer’s disease pathology will never develop symptoms.

“This test has the potential for causing a lot of concern for people who take the blood test and haven’t got any symptoms and become anxious,” he said.

He said such people may be at higher risk of developing Alzheimer’s disease, but will not necessarily go on to have the condition.

As a result, there are pitfalls associated with tests being made available commercially, he said.

“I’m concerned. People will turn up very, very worried with the test that shows they’ve got the pathology,” he said.

“If people are worried, there’s no substitute for going to their doctor and having a proper consultation and examination organised.”

He said the test would be best used on patients who already have dementia as it allows doctors to determine whether Alzheimer's disease is the cause of their symptoms.

Having tests that identify people who may not go on to become ill is something seen with other conditions, Dr Koychev said, giving the example of prostate cancer.

With this condition, a blood test called PSA can identify cases that are not likely to be harmful to the patient, sometimes leading to what is termed overdiagnosis and unnecessary treatments. The PSA test also has the drawback of missing some cases that do prove to be harmful.