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.