A blood test that can detect signs of Alzheimer's up to 20 years before the onset of symptoms is a step closer to being developed, according to scientists in the US.

Researchers in St Louis have discovered a way to measure how much of the damaging protein linked to the disease has built up on the brain.

They say the test is 94% accurate when taking age and genetic risk factors into account; after 65, the chances of developing dementia doubles every five years.

Image: Scientists hope a blood test will become available to GPs within a few years

The report, published in medical journal Neurology, also found initial blood tests had flagged early signs of dementia, which brain scans had missed.

It says the test's benefits will be much greater once there are treatments to stop the disease process and prevent Alzheimer's.


Clinical trials of preventive drug candidates have been hampered by the difficulty of finding participants who have had changes in the brain but have no cognitive problems.

The blood test could provide a way to efficiently screen for people with early signs of the disease so they can take part in trials looking at whether drugs can prevent it.

Senior author Randall J Bateman, professor of neurology in Washington University's medical school, said: "Right now, we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years.

"But with a blood test, we could potentially screen thousands of people a month.

Image: After 65, the chances of developing Alzheimer's doubles every five years. File pic

"That means we can more efficiently enrol 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."

There is growing consensus among neurologists that Alzheimer's treatment needs to begin as early as possible, ideally before any cognitive symptoms arise.

By the time people show signs of the disease, their brains are so severely damaged that no therapy is likely to fully heal them.

Researchers say they hope a blood test will become available to GPs within a few years.