A simple blood test is being developed that could detect Alzheimer's disease years before the classic symptoms of memory loss and dementia appear.

Preliminary results show that the test is more than 90 per cent accurate and can detect Alzheimer's up to six years before symptoms emerge. However, further work is needed before the test could be used to diagnose real patients.

Professor Tony Wyss-Coray of Stanford University Medical Centre in California investigated changes to a set of proteins in the blood which they used as markers for the alterations to the chemistry of the brain that precede Alzheimer's.

The proteins are involved in communication between the cells of the body and the scientists found that shifts in the patterns of "dialogue" can indicate the changes in the brain that accompany the onset of Alzheimer's.

The study is published in the journal Nature Medicine.