Scientists have developed a new blood test that could detect whether or not a person will develop dementia within three years.
Changes in the blood may signify Alzheimer's disease in its earliest stages, researchers found.
A new study, published in the journal Nature Medicine, identified 10 molecules in blood could be used to predict with at least 90 per cent accuracy whether people will go on to develop mild cognitive impairment or Alzheimer's disease.
It is the first research which has been able to show differences in biomarkers in the blood between people with Alzheimer's disease before the symptoms occur and people who will not go on to develop the condition.
The finding has potential for developing treatment strategies for Alzheimer's at an earlier stage - when therapy would be more effective at slowing or preventing onset of symptoms, the authors said.
Researchers from Georgetown University Medical Centre in the US examined 525 healthy participants aged 70 and over and monitored them for five years.
During the research, 28 participants went on to develop the conditions and 46 were diagnosed at the start of the study.
Mid-way through the research, the authors analysed 53 patients who already had one of the conditions and 53 "cognitively normal" people.
They discovered 10 molecules which appeared to "reveal the breakdown of neural cell membranes in participants who develop symptoms of cognitive impairment or Alzheimer's disease".
They then tested other participants' blood to see whether these biomarkers could predict whether or not they would go on to develop the conditions.
By measuring the presence of 10 compounds the researchers could predict with 90 per cent accuracy people that would go on to suffer from mild cognitive impairment (MCI) or Alzheimer's disease (AD).
"Our novel blood test offers the potential to identify people at risk for progressive cognitive decline and can change how patients, their families and treating physicians plan for and manage the disorder," said one of the study's authors, Professor Howard Federoff.