Scientists in Australia are working on a blood test that could lead to routine screening for Alzheimer`s disease.

They have identified blood-based signs of plaque in the brain that could alert doctors to the disease long before symptoms appear and irreversible brain damage has occurred.

"Early detection is critical. It gives people a much better chance of receiving treatment before it`s too late," researcher Dr Samantha Burnham from CSIRO`s Preventative Health Flagship said.

Dr Burnham hopes the breakthrough will lead to routine age-based testing in five to 10 years.

Early diagnosis would also allow people to develop a care plan to reduce the burden on the patient and their family, she said.

She said that a blood test would be the ideal first stage to help identify people at risk before a diagnosis is confirmed with cognitive tests and brain scans.

The research has been published in the journal Molecular Psychiatry.