A new blood test from Quest Diagnostics has Alzheimer's experts concerned.
The Quest AD-Detect test, which consumers can now , measures amyloid-beta 42 and amyloid-beta 40 in blood to provide an amyloid-beta 42/40 ratio. In theory, the ratio may help identify the risk of developing Alzheimer's disease. In practice, the value of the Quest test is unknown.
The test has by FDA.
"There are no large-scale, long-term clinical trials that support the idea that the AD-Detect test can predict whether a cognitively unimpaired person will transition to cognitively impaired," said Rebecca Edelmayer, PhD, senior director of scientific engagement at the Alzheimer's Association in Chicago.
"As a result, it is unclear what the results of this test may mean about your Alzheimer's risk or your health status," Edelmayer told 鶹ý. While some blood tests show promise for improving the diagnostic work-up for Alzheimer's disease, "there is a lack of data to support the broad use of these tests in primary care settings, let alone individually by consumers at home," she pointed out.
"As such, the Alzheimer's Association does not endorse the use of AD-Detect by consumers," Edelmayer stated. "We challenge Quest to pursue a path of FDA approval that demonstrates, rigorously, that this test is valuable to clinicians and patients as part of the diagnostic process."
Research groups in several countries are working together to establish validated blood-based tests to detect Alzheimer's pathology that include , noted Suzanne Schindler, MD, PhD, of Washington University in St. Louis, who studies Alzheimer's disease biomarkers.
"Quest has not participated in any of these efforts," Schindler told 鶹ý. "They seem to be working hard on marketing to consumers but have made little to no attempt to rigorously validate their assays in a transparent way. What they are marketing is far outside of the recommended use of Alzheimer's disease blood-based biomarkers."
According to the Alzheimer's Association, the for validated blood-based biomarkers at specialized memory clinics is for the diagnostic work-up of patients with cognitive symptoms, and the results should be confirmed with cerebrospinal fluid (CSF) analysis or PET scans if possible. Blood-based tests are used in a few to help screen eligible participants. Tests involving plasma tau also are being investigated as predictors of cognitive decline.
Once well-validated blood-based biomarkers demonstrate equivalent performance to CSF analysis or PET scans, these recommendations may change, Schindler noted.
"It is not currently recommended to use Alzheimer's disease blood tests in asymptomatic individuals, as this could expose them to adverse consequences -- for example, ineligibility for long-term care insurance -- and they are not yet eligible for treatments," she said.
Consumers pay for the $400 test online; a telehealth doctor then reviews the purchase and places an order on their behalf. Patients visit a local Quest Diagnostics lab for a blood draw. They can read their test results online and have the option to speak with a physician when their results are in.
No peer-reviewed research papers validating the AD-Detect test have been published, but an presented by Quest at the 2022 Alzheimer's Association International Conference (AAIC) provided preliminary data. A Quest representative told 鶹ý that the sensitivity and specificity data reported in the 2022 abstract were incorrect and the company is working to change those figures on the AAIC site.
The assay uses liquid chromatography and mass spectrometry and has been verified according to Clinical Laboratory Improvement Amendments () regulations.
AD-Detect is not a diagnostic test, Quest said. It is marketed to anyone 18 and older who has a family history of Alzheimer's disease, has had brain trauma or a head injury, is experiencing memory loss, or is experiencing early cognitive decline.
When used carefully, Alzheimer's disease blood tests can be used to help patients, "but if used inappropriately, they could cause significant anxiety and confusion," Schindler cautioned.
"Physicians are sometimes confused about how to interpret these tests," she said. "I know that patients will have a difficult time knowing what the results mean, and many patients will draw the wrong conclusions."