A new test that measures key proteins in the blood has shown to be much more accurate than doctor assessments in identifying Alzheimer’s disease in people with early-stage illness.
The test, called APS2 (the amyloid probability score 2), achieved 91% accuracy in diagnosing Alzheimer’s in individuals with mild cognitive decline or early dementia, compared to the 61% success rate of primary care doctors who evaluated the same patients.
Although the test is not yet approved for routine use, Dr. Teresa D’Amato, director of geriatric emergency medicine at Northwell Health in Forest Hills, NY, expressed great excitement about the findings.
“This blood test would be great as a first round of diagnostic testing because it looks like it’s pretty accurate,” she said.
The study’s results were published on July 28 in the Journal of the American Medical Association. A team of dementia experts who wrote an editorial accompanying the research believe that an accurate, easily administered blood test for Alzheimer’s could be a significant breakthrough.
They stressed that diagnosing Alzheimer’s is challenging, especially in primary care, and having a reliable blood test is essential to help primary care physicians make early and accurate diagnoses.
The editorialists included Dr. Stephen Salloway of Brown University, Dr. Christopher Rowe of the University of Melbourne, Australia, and Dr. Jeffrey Burns of the University of Kansas Medical Center.
The APS2 test was developed by a team led by Dr. Sebastian Palmquist from Skane University Hospital and Lund University in Malmo, Sweden. The urgency for a more accurate diagnostic test has increased due to the advent of drugs that can slow Alzheimer’s in its earliest stages.
“It becomes really important to diagnose Alzheimer’s very early on to make these folks eligible for possible treatment,” Dr. D’Amato said.
The test works by measuring the levels of two types of proteins in the blood: tau and amyloid. These proteins’ buildup in the brain is a hallmark of Alzheimer’s. In the study, 1,213 patients with cognitive symptoms were evaluated either through a standard primary care physician exam or the APS2 test.
The patients were around 74 years old on average. Of these, 23% had subjective cognitive decline, 44% had mild cognitive impairment, and 33% had already been diagnosed with dementia.
Patients were assessed by primary care physicians using standard criteria, CT scans, and cognitive tests, while also receiving the APS2 blood test. The results from each method were compared to “gold standard” tests for Alzheimer’s, which include cerebrospinal fluid tests and PET scans looking for amyloid and tau in the brain.
The APS2 test demonstrated 91% accuracy in identifying Alzheimer’s, compared to 61% for primary care doctors and 73% for dementia specialists.
The study found that measuring tau protein levels alone produced an equally high accuracy (90%) in diagnosing Alzheimer’s.
However, the researchers and editorial authors noted several unanswered questions: Would the test be economical for use in doctors’ offices? Will it gain FDA approval? And will it be surpassed by other Alzheimer’s blood tests currently in development?
Despite these questions, the editorial authors believe that the study makes a convincing case that highly sensitive blood measures of Alzheimer’s disease can be integrated into clinical decision-making, including in primary care settings.
Dr. D’Amato explained that the envisioned use of the test would involve a physician conducting standard blood work to rule out other causes of cognitive decline, in addition to the new blood tests for amyloid and tau.
While the APS2 test holds promise, Dr. Palmquist’s team emphasized that a blood test alone will never be sufficient to diagnose Alzheimer’s early. Alzheimer’s can take years to develop in the brain, and symptoms that resemble early Alzheimer’s can also be caused by other conditions.
“Incorrect interpretation of a positive Alzheimer disease biomarker [test] could thus lead to under-diagnosis of relatively common non-Alzheimer disease conditions,” the study authors noted.
Overall, the APS2 test could be an exciting tool in diagnosing Alzheimer’s sooner and more accurately, potentially opening the door to earlier and more effective treatments.
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The research findings can be found in JAMA.
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