Thursday, September 14, 2023

Multiple Articles: Concerns about Quest LDT Alzheimer Blood Test?

FDA-approved Amyvid (PET Scan) advertised next to LDT article

Multiple news articles this week quote experts as expressing concern about an LDT (lab-developed test) being marketed as an Alzheimer diagnostic.   The test is a blood test; the only FDA-validated tests for Alzheimer's so far have been PET scans and CSF tests.

See an article from Reuters here.  With remarks such as, "Dr. Sarah Kremen, a neurologist at Cedars-Sinai in Los Angeles, was concerned that people who test positive but have no symptoms will come in seeking further testing."

See an article at MedPage here.  With remarks such as, "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/"

The longest article, by Adam Bonislawski, is by subscription at 360Dx.  With remarks such as, "mass spec-based assays for Aβ 42/40 ratio have higher performance ... than do immunoassays, but "you have to be very rigorous about" your measurements, said Suzanne Schindler, associate professor of neurology at the Washington University School of Medicine. "There's only about a 10 percent difference between positives and negatives, and so if you are off by a little bit or your assay drifts, then you can really misclassify a lot of people," she said, adding that Quest has released little data on the analytical and clinical performance of its test. [The article continues, "At the 2022 Alzheimer's Association International Conference, Quest presented a poster on AD-Detect, and said it aims to publish data on the test in a peer-reviewed publication."]


The test is NY State approved; search for analyte amyloid and facility Quest, here.

The test is stated in an article above to be 71% specific, which could mean about 1 in 3 would get a false positive, although the negative and positive predictive values are highly dependent on the test population (population spectrum).   One historical problem - not necessarily relevant here - is Alzheimer tests over the decades that were validated on 100 perfect controls and 100 perfect Alzheimer cases, but then perform much worse on the real world and borderline patients who actually need testing.  


AI Corner:

ChatGPT reviews the three articles, then describes them in the satirical voice of Louis Black, here.