Scientists are closer to rolling out a revolutionary blood test for Alzheimer’s after discovering a new way of detecting one of the earliest signs of the brain disease.

For decades scientists worldwide have tried to develop blood tests to predict Alzheimer’s in the hope of replacing the expensive and often invasive brain scans and lumbar punctures currently used to diagnose the most common form of dementia.

A team of Australian and Japanese scientists now claim they have the most accurate test yet for the earliest indicator of Alzheimer’s – a build-up of an abnormal protein in the brain known as beta-amyloid.

One of the lead researchers Colin Masters, a laureate professor of neuroscience at the Melbourne-based Florey Institute, says the blood test is more than 90% accurate at predicting Alzheimer’s, based on a study involving 252 Australian and 121 Japanese patients.

It can detect the build up of beta-amyloid in people without any outward signs of Alzheimer’s including memory loss, as well those with moderate symptoms and full onset dementia.

“By the time you hit 60 to 70 about 30% of the population are showing signs of this protein aggregating in their brain and that can be picked up now with this blood test,” Prof Masters told reporters.

“I can see in the future, five years from now, where people have a regular checkup every five years after age 55 or 60 to determine whether they are on the Alzheimer’s pathway or not.”

Alzheimer’s starts developing about 30 years before obvious symptoms emerge.

While up to 40% of Australians over 70 are considered at risk of Alzheimer’s, drug companies haven’t had much success tackling its underlying causes.

The new blood test has boosted hopes that it could help the development of new drugs because of its ability to identify people most at risk of Alzheimer’s - the perfect participants for clinical trials of new therapies.

It could also give those at risk of Alzheimer’s a valuable headstart in slowing its onset by adjusting their sleep, exercise and diet.

“If a person knows they are on this pathway well before the onset of any cognitive impairment some would want to alter their lifestyles,” Prof Masters said.

Details of the new test, which was developed by Nobel prize-winning scientist Dr Koichi Tanaka at Japanese medical technology company Shimadzu Corporation, were published in the prestigious journal Nature on Thursday.

Using high-tech mass spectrometry techniques, the Japanese and Australian scientists identified patients with a rouge peptide in their blood plasma, indicating a build-up of beta-amyloid in the brain.

Prof Masters, who has spent 30 years researching an Alzheimer’s test, said mass spectrometry was more sensitive and accurate at detecting beta-amyloid levels than PET brain scans and lumbar punctures.

While more tests are needed, the new technique may one day also help determine how fast a patient with Alzheimer’s may deteriorate, and tell how effective future drugs are at clearing beta-amyloid buildups.