Scientists say an accurate blood test which helps detect the formation of amyloid beta proteins in the brain will allow them to identify patients who are on track to develop Alzheimer's disease decades before symptoms appear. At present the only way to detect amyloid beta build up in the brain is via complex and costly PET scans.
Researchers from Washington University School of Medicine, in St Louis, Missouri, writing in the journal Neurology*, measured levels of amyloid beta in the blood of 158 adults aged over 50 to see if these matched levels found in brain scans. It did, but only 88% of the time - which is not accurate enough for a diagnostic test.
When the researchers combined this information with two other risk factors for the disease - an age of over 65 and people with a genetic variant called APOE4, which at least triples the risk of the disease - the accuracy of the blood test improved to 94%.
They say that being able to identify people on track to develop Alzheimer's could help the progress of drug trials.
Senior study author Randall J Bateman, professor of neurology, said this could now help screen many more people than expensive brain scans.
"That means we can more efficiently enrol participants in clinical trials, which will help us find treatments faster, and could have an enormous impact on the cost of the disease as well as the human suffering that goes with it," he said.
Participants in trials must have early Alzheimer's brain changes - such as build-up of amyloid - but no cognitive problems as yet.
UK experts said the results were promising - and a step towards a reliable blood test for Alzheimer's to speed up dementia research. But larger studies were needed first.
Dr Sara Imarisio, from Alzheimer's Research UK, said: "Improving the accuracy of blood tests has long been a goal for researchers and using additional information about genetic risk to bolster a test like this is an encouraging step forward.
"Now is a critical time to invest in research to realise the possible benefits of a blood test for Alzheimer's and begin to test potential life-changing drugs earlier."
*E. Schindler SE, Bollinger JG, Ovod V, et al. High-precision plasma β-amyloid 42/40 predicts current and future brain amyloidosis. Neurology Aug 2019; DOI: 10.1212/WNL.0000000000008081