Researchers believe they are closer to developing a blood test that could diagnose Alzheimer's.
There is no definitive test for the brain-wasting disease. Doctors rely on cognition tests and brain scans.
A technique published in the journal Genome Biology showed differences in the tiny fragments of genetic material floating in the blood could be used to identify patients.
The test was accurate 93% of the time in trials on 202 people.
One of the main goals of Alzheimer's research is to find ways of detecting the disease earlier.
It starts years before symptoms appear and it is thought that future treatments will need to be given before large parts of the brain are destroyed. This will require new ways of testing for the condition.
The team at the Saarland University, in Germany, analysed 140 microRNAs (fragments of genetic code) in patients with Alzheimer's disease and in healthy people.
They found 12 microRNAs in the blood which were present in markedly different levels in people with Alzheimer's. These became the basis of their test.
Early trials showed it was successful and was "able to distinguish with high diagnostic accuracies between Alzheimer's disease patients and healthy" people.
However, more research to improve accuracy and to see whether it would work in the clinic is still needed before the test would be considered as a way of diagnosing patients.
Dr Eric Karran, from the charity Alzheimer's Research UK, said: "This is an interesting approach to studying changes in blood in Alzheimer's and suggests that microRNAs could be playing a role in the disease.
"The findings highlight the importance of continuing research efforts to understand the contribution of microRNAs to Alzheimer's, but the translation of this into a blood test for Alzheimer's in the clinic is still some way off.
"A blood test to help detect Alzheimer's could be a useful addition to a doctor's diagnostic armoury, but such a test must be well validated before it's considered for use. We need to see these findings confirmed in larger samples and more work is needed to improve the test's ability to distinguish Alzheimer's from other neurological conditions."