Melbourne researchers have developed a blood test to diagnose early onset Alzheimer's disease.

A blood test that can detect Alzheimer's disease years before symptoms appear has been developed by Victorian researchers.

This blood test could be crucial to the development of therapeutic and preventative drugs for Alzheimer's, says lead researcher Professor Andrew Hill of the University of Melbourne.

The neurodegenerative disorder is one of the biggest health concerns facing Australians.

"Our unique study has found that in a certain fraction of the blood there are small genes called microRNAs, and there are about 2000 of those in humans, and we've identified 16 that are changed in people with Alzheimer's compared to healthy people," said Prof Hill.

The team from the University of Melbourne had previously discovered they could detect Alzheimer's 20 years before it appeared by using expensive brain-imaging tests.

But in this new study they show how a simple, cost-effective blood test can also predict the disease.

For the study, published in the journal Molecular Psychiatry, they analysed the blood of 110 people, investigating the differences in the tiny fragments of genetic material floating in the blood to identify patients with future Alzheimer's.

As a result of the blood tests they found a number of healthy aged participants tested positive.

They then assessed these patients using brain-imaging techniques, which showed signs of degeneration in the brain resembling Alzheimer's features.

"What we've done is identified a panel of microRNAs that are different in Alzheimer's patients to control, and these patients have been brain-imaged and we are very confident they have Alzheimer's disease," said Prof Hill.

The blood test has the potential to improve prediction for the disease to 91 per cent accuracy, he said.

Earlier this year researchers from King's College London and the University of Oxford found a panel of 10 proteins that could predict those who would develop dementia in the next year with 87 per cent accuracy.

But Prof Hill says a blood test that looks for microRNAs is easier to perform than one that searches for protein biomarkers.

"We are hoping that this test in combination with something like cognitive testing might indicate who should have a brain scan, which can only be performed in certain centres at the moment and cost quite a lot of money.

"We are hoping this might be a relevant pre-screen to help determine who should go and have the more detailed imaging studies."

Copyright AAP 2014.