Scientists may have moved one step closer to detecting Alzheimer’s disease long before symptoms appear, according to a new study published in The Lancet.

Researchers led by the University of California, San Francisco found that specific blood biomarkers associated with Alzheimer’s were linked to subtle cognitive changes in middle-aged adults who did not have dementia.

The study examined 1,350 adults in the United States with an average age of 61. Researchers measured blood levels of biomarkers linked to beta-amyloid proteins — Aβ42 and Aβ40 — as well as the protein p-tau217, all of which are associated with Alzheimer’s disease.

The biomarkers are used to measure tau protein accumulation and amyloid plaques, two key biological features of Alzheimer’s.

According to the findings, higher levels of these biomarkers were associated with lower performance in two important cognitive areas: processing speed and executive brain function, which includes planning, maintaining attention and adapting to new challenges.

Researchers said the results demonstrate the potential for detecting Alzheimer’s at a very early stage through blood testing, even before dementia symptoms develop.

The study’s authors also noted that up to 40% of dementia cases could potentially be prevented or delayed through the management of risk factors linked to the disease.

However, experts who were not involved in the study urged caution over the broader use of such tests.

In an accompanying commentary, Anna Rosenberg of Sweden’s Karolinska Institute and Tiia Ngandu of the Finnish Institute for Health and Welfare warned that blood tests for Alzheimer’s-related proteins in younger people without cognitive impairment could produce a higher rate of false positive results.

They stressed that additional diagnostic criteria should always be used alongside blood tests and noted that these biomarkers are not suitable for large-scale screening in populations without cognitive symptoms.