Blood test can pick up Alzheimer's disease before symptoms show with 94 per cent accuracy

Scientists now know that amyloid is already building up in the brain up to twenty years before any symptoms show, which can be seen on brain scans. Photo / 123RF

A blood test has been found to be 94 per cent accurate at detecting Alzheimer's disease before people develop memory loss and confusion.

Researchers from Washington University School of Medicine in St. Louis can now measure tiny levels of amyloid beta protein in the blood, and use levels to predict how much has accumulated in the brain.

Although the causes of Alzheimer's are still unknown, the disease leads to a build up of sticky amyloid plaques in the brain, which prevent neurons from communicating with each, setting off a cascade of further damage.

But scientists now know that amyloid is already building up in the brain up to twenty years before any symptoms show, which can be seen on brain scans.

Researchers found that when blood amyloid levels are combined with two other major risk factors - age and the presence of the gene mutation APOE4 - scientists could spot the disease before it emerged.

The test is important because many scientists now believe that the brain damage of Alzheimer's is impossible to reverse and are now mostly looking for drugs which would prevent the harm from occurring in the first place.

And if scientists knew who would get the disease they could carry out trials on preventative drugs which could stop the condition from ever developing.

"Right now we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years," said senior author Dr Randall Bateman, Professor of Neurology.

"But with a blood test, we could potentially screen thousands of people a month. That means we can more efficiently enroll participants in clinical trials, which will help us find treatments faster, and could have an enormous impact on the cost of the disease as well as the human suffering that goes with it."

Around 800,000 people have dementia in Britain, and despite decades of trials there are still no drugs to help patients.

The new study involved 158 adults over age 50 and all but 10 were cognitively normal. Each provided at least one blood sample and underwent one PET brain scan, can currently be used to spot early changes in the brain up to twenty years early.

The researchers classified each blood sample and PET scan as amyloid positive or negative, and found that the blood test from each participant agreed with his or her PET scan 88 percent of the time, which is promising but not accurate enough for a clinical diagnostic test.

In an effort to improve the test's accuracy, the researchers incorporated several major risk factors for Alzheimer's.

Age is the largest known risk factor; after age 65, the chance of developing the disease doubles every five years. A genetic variant called APOE4 also raises the risk of developing Alzheimer's three- to fivefold. When the researchers included these risk factors in the analysis, they found that age and APOE4 status raised the accuracy of the blood test to 94 per cent.

The changes are known to begin up to twenty years early so the test could predict who would get the disease decades before symptoms began.

Commenting on the research Dr Sara Imarisio, Head of Research from Alzheimer's Research UK, said: "Alzheimer's brain changes begin decades before dementia symptoms start to show and life-changing drugs are likely to be most effective at these early disease stages.

"An accurate and reliable blood test for Alzheimer's that can pick up these early changes could revolutionise dementia research and dramatically improve how we select people for early-stage drug trials."

The findings were published in the journal Neurology.