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 that 10 molecules in blood could be used to predict with at least 90% accuracy whether people would go on to develop mild cognitive impairment or Alzheimer's disease.
It is the first research that 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 the 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. A clinical trial is now being planned.
Dr Simon Ridley, head of research at charity Alzheimer's Research UK, said: "Alzheimer's disease begins to develop long before symptoms such as memory loss appear, but detecting the disease at this pre-symptomatic stage has so far proved difficult.
"More work is needed to confirm these findings, but a blood test to identify people at risk of Alzheimer's would be a real step forward for research."
Dr Doug Brown, director of research and development at the Alzheimer's Society, added: "Having such a test would be an interesting development, but it also throws up ethical considerations. If this does develop in the future, people must be given a choice about whether they would want to know."