A Quest Diagnostics Alzheimer’s blood test that people could purchase from home without visiting a doctor first is no longer being marketed directly to consumers.
The test, known as Quest AD-Detect, measures amyloid-beta 42 and amyloid-beta 40 in blood to provide an amyloid-beta 42/40 (AB 42/40) ratio.
Quest Diagnostics first announced AD-Detect as a consumer-initiated test on July 31, 2023, but the test is no longer offered on the company’s consumer platform.
“We paused offering our consumer-initiated AB 42/40 test at the end of 2023, in part to redouble our focus on our primary physician channel,” a Quest Diagnostics representative told MedPage Today.
The decision followed multiple communications involving Quest, the Alzheimer’s Association, and biomarker researchers.
AD-Detect has not been cleared or approved by the FDA. It is still being marketed to physicians, though no peer-reviewed research papers validating its accuracy have been published.
Preliminary data supporting AD-Detect were presented in an abstract at the 2022 Alzheimer’s Association International Conference, from a study of 209 people. In August 2023, after MedPage Today raised questions about the data, the abstract authors said the sensitivity and specificity estimates were inadvertently switched.
On Aug. 21, 2023, the abstract was amended to include a new sentence that stated that, at the amyloid-beta 42/40 cut-point of 0.160, “the assay has a sensitivity of 89% and specificity of 71% for detecting PET-positivity, which is suggestive of AD [Alzheimer’s disease].”
Alzheimer’s experts on the Alzforum networking site maintained that the specificity numbers weren’t good enough.
“With the type of patients that Quest seems to be targeting with their low specificity test, a positive test result may be false-positive more often than it is true-positive,” Suzanne Schindler, MD, PhD, of Washington University in St. Louis, told MedPage Today. “This could cause unnecessary patient anxiety and further burden memory clinics that are already stretched thin.”
AD-Detect is not a diagnostic test, Quest said. It is a laboratory-developed test (LDT) that uses liquid chromatography and mass spectrometry. LDTs like Quest AD-Detect are regulated by the Clinical Laboratory Improvement Amendments (CLIA) program of the Centers for Medicare & Medicaid Services, which does not address the clinical validity of any tests.
The FDA recently proposed changes to LDT oversight, expressing concern that patients who use them for Alzheimer’s disease, cancer, heart disease, and other disorders could initiate unnecessary treatment or delay or forgo proper treatment based on inaccurate LDT results.
“These widely used tests are not generally coming to the FDA for review or otherwise complying with FDA requirements,” FDA Commissioner Robert Califf, MD, said when the agency’s proposal was announced last September.
“This leaves Americans vulnerable to making important healthcare choices based on potentially faulty or inaccurate test results,” Califf pointed out. “This should not continue.”
The Alzheimer’s Association currently is updating its appropriate use recommendations for blood tests in Alzheimer’s disease. The group calls for cautious use of validated blood-based biomarkers at specialized memory clinics as part of the diagnostic work-up of patients who have cognitive symptoms, with results confirmed with cerebrospinal fluid (CSF) analysis or PET scans.
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