A blood test that identifies patients likely to develop Alzheimer's Disease could be available in two years, according to scientists.

The test, which works long before there are recognisable symptoms, is almost 90% accurate, new research shows.

And the inventors believe it would allow drugs to be tested in the early stages of the disease, in the hope of delaying or even stopping further deterioration.

Professor Simon Lovestone, who devised the test at King's College London said "A drug that worked in that preclinical phase would feel like prevention. You would go to your doctor take a drug and in effect you would have the clinical symptoms prevented - even if the clinical disease had started in your brain".

Doctors know that Alzheimer's starts to affect the brain at least 10 years before there are outward signs of the disease.

The new test identifies 10 key proteins in the blood of patients with Mild Cognitive Impairment who will go on to develop Alzheimer's in the next year. Results of a major trial published in the journal Alzheimer's & Dementia show the test is 87% accurate.

"Alzheimer's begins to affect the brain many years before patients are diagnosed" said Professor Lovestone.

"Many of our drug trials fail because by the time patients are given the drugs, the brain has already been too severely affected. A simple blood test could help us identify patients at a much earlier stage".

But Dr. Eric Karran, science director with Alzheimer's Research UK which funded the study, cautioned that it needs further refinement before being used by GPs to routinely diagnose the disease.

He said "You have false positives, which is where the test says you are liable to get Alzheimer's disease but in fact the test is wrong. If this was some benign condition one wouldn't be bothered".

"But we know that Alzheimer's Disease is the most feared diagnosis. So it is very important to understand that point".

Vivienne Hill was devastated that doctors could do nothing to slow her mother Mary's symptoms. She welcomed the new research.

"We knew she was going to slowly deteriorate from a vibrant happy woman to someone who was bedridden for the last three years of her life who could not talk or do anything for herself" she said.

"It's horrible knowing that".