Tests carried out on humans suggest people with Alzheimer's disease could be diagnosed before symptoms start to appear, US doctors say.
Patients are often not diagnosed until the later stages, after brain damage.
But researchers said a sensitive test to detect a type of protein molecule could identify the disorder early after successfully trialling it on 30 people.
The team at Northwestern University in Chicago have claimed Alzheimer's could be treated if caught early.
Lead researcher William Klein said traditional diagnosis came too late for people with Alzheimer's.
The team believes molecules, called ADDLs, are present at high levels in the cerebrospinal fluid at the onset of Alzheimer's and block memory function, the Proceedings of the National Academy of Sciences reported.
Using a highly sensitive test, which employs bionanotechnology, the team was able to check the levels of ADDL in 30 individuals and found they were consistently higher in people with the disease.
Alzheimer's Research Trust deputy chief executive Harriet Millward said an accurate test for Alzheimer's in the early stages would help treatment, but she said there was still a long way to go.