There is much excitement and concern this morning about a blood test that US researchers claim could predict with greater than 90% accuracy if a healthy person will develop dementia within three years.

The study, published in Nature Medicine, saw researchers at Georgetown University Medical Center (GUMC) adopt a "lipidomic approach to detecting preclinical Alzheimer's disease in a group of cognitively normal older adults". Specifically, they measured the presence of ten compounds called phospholipids in the blood  of 525 healthy participants aged 70 and over and observed them for five years.

Over the course of the study, 74 participants met the criteria for either mild AD or a condition known as amnestic mild cognitive impairment (aMCI), in which memory loss is prominent. Of these, 46 were diagnosed upon enrollment and 28 developed aMCI or mild AD during the study.

In the study’s third year, the researchers selected 53 participants who developed aMCI/AD (including 18 converters) and 53 cognitively normal matched controls for the lipid biomarker discovery phase of the study. The lipids were not targeted before the start of the study, but rather, were an outcome of it.

This is the first known published report of blood-based biomarkers for preclinical AD and the test could be ready for use in clinical studies in as few as two years. Howard Federoff, professor of neurology at GUMC, said the novel blood test "offers the potential to identify people at risk for progressive cognitive decline and can change how patients, their families and treating physicians plan for and manage the disorder".

Prof Federoff noted that there have been many efforts to develop drugs to slow or reverse the progression of AD but all of them have failed perhaps because therapies were evaluated too late in the disease process. “The preclinical state of the disease offers a window of opportunity for timely disease-modifying intervention,” he added, and “biomarkers such as ours that define this asymptomatic period are critical for successful development and application of these therapeutics".

Ethical considerations

Commenting on the data, Doug Brown, R&D director at the Alzheimer's Society in the UK, said that "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, and fully understand the implications."

He went on to say that this research "could also give clues on how AD occurs and warrants further study, but as such a small number of people showed dementia symptoms there need to be larger studies with different populations before it could be turned into a blood test for AD".