The traditional medical screening for people suspected of having Alzheimer’s could be replaced by a new test that measures levels of key proteins in the blood and has been shown to be much more accurate at detecting the disease than currently available assessments.
The test is called APS2 (amyloid probability score 2) and is 91 percent accurate at diagnosing Alzheimer’s in people with mild cognitive impairment or early dementia, compared with a 61 percent success rate for primary care physicians who tested the same patients. The findings were published July 28 in the Journal of the American Medical Association.
The new generation of drugs that slow the progress of Alzheimer’s when it is detected in its early stages has made the search for an easier and more accurate diagnostic test even more urgent. Such a test is not yet approved for routine use, but having an accurate and easy-to-administer blood test could be a game-changer, say a team of dementia experts who wrote an editorial accompanying the research.
“Diagnosing Alzheimer’s is challenging, especially in primary care. Having a reliable blood test is essential to help primary care physicians make an early and accurate diagnosis,” the editorialists noted. They include 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.
Blood levels of proteins associated with Alzheimer’s
The new test was developed by a team led by Dr Sebastian Palmquist of Skane University Hospital and Lund University in Malmö, Sweden, and is based on relative blood levels of two types of proteins whose build-up in the brain has long been a hallmark of Alzheimer’s: tau “tangles” and amyloid “plaques.”
Research into this innovative blood test method, which measures levels of plasma Phospho-Tau217, began in 2019. Studies indicate that the blood test can detect Alzheimer’s-related changes before symptoms are apparent and track progression as the disease progresses. Earlier this year, results showed that this blood test is as reliable as cerebrospinal fluid tests (and in some cases superior) in diagnosing this dementia. The current study demonstrates for the first time the reliability of the test when used in routine healthcare settings, both in primary and specialist care.
In the study, 1,213 people with mild memory symptoms and an average age of 74 were screened either through a standard exam by a primary care physician or by using the APS2 test. Overall, 23% had “subjective cognitive impairment,” 44% had “mild cognitive impairment,” and 33% had already been diagnosed with dementia. The results of each of these screening methods were compared to the “gold standard” tests for Alzheimer’s (cerebral spinal fluid tests and PET scans that look for amyloid and tau in the brain).
According to the researchers, the APS2 was found to be 91 percent accurate at detecting Alzheimer’s disease in patients, compared with 61 percent accuracy for primary care physicians. The blood test even outperformed dementia specialists: They were correct in 73 percent of their diagnoses compared with the blood test’s 91 percent accuracy. Of the two proteins measured by the test, Tau appeared to be the more important. In fact, looking at Tau protein measurements alone yielded similarly high accuracy (90 percent) in diagnosing Alzheimer’s disease.
“The blood test even outperformed dementia specialists: they were correct in 73% of their diagnoses compared to the 91% accuracy of the APS2 test.”
“The blood test can determine with 90% accuracy whether a person suffering from memory loss has Alzheimer’s,” said Sebastian Palmqvist, associate professor of neurology at Lund University and consultant at Skåne University Hospital, who led the study together with Professor Oskar Hansson.
“The accuracy of primary care physicians in identifying Alzheimer’s disease was 61%, while specialist physicians were correct 73% of the time. This underlines the lack of good and cost-effective diagnostic tools, especially in primary care, and indicates the potential improvement in diagnosis with the adoption of this blood test in healthcare settings,” added Sebastian Palmqvist.
“Early diagnosis is crucial when it comes to developing new treatments that slow the progression of the disease,” explains Professor Hansson. “For example, two immunotherapies have recently been approved in the US and are expected to be available in Europe shortly. Early and accurate diagnosis is also vital to facilitate research into new treatments.”
The simplicity and reliability of this blood test represent a significant advance in the diagnosis of Alzheimer’s, offering a simple method to rule out the disease in primary care. This is crucial, as memory loss can also be caused by other treatable diseases, such as depression or chronic fatigue.
“Next steps include establishing clear clinical guidelines for the use of the blood test in healthcare,” Hansson concludes. “The test is already available in the US and is likely to be available in many other countries soon. Initially, it will be used primarily in specialist memory clinics, and it may take about one to two years to implement the guidelines and training in primary care.”
